[InstCombine] Don't sink if it would require dropping deref assumptions. #166945

fhahn · 2025-11-07T14:43:34Z

Currently sinking assumes in instcombine drops assumes if they would prevent sinking. Removing dereferenceable assumptions earlier on can inhibit vectorization of early-exit loops in practice.

Special-case deferenceable assumptions so that they block sinking. This can be combined with a separate change to drop dereferencebale assumptions after vectorization: https://clang.godbolt.org/z/jGqcx3sbs

Not sure if there is a better solution.

llvmbot · 2025-11-07T14:44:10Z

@llvm/pr-subscribers-llvm-transforms

Author: Florian Hahn (fhahn)

Changes

Currently sinking assumes in instcombine drops assumes if they would prevent sinking. Removing dereferenceable assumptions earlier on can inhibit vectorization of early-exit loops in practice.

Special-case deferenceable assumptions so that they block sinking. This can be combined with a separate change to drop dereferencebale assumptions after vectorization: https://clang.godbolt.org/z/jGqcx3sbs

Not sure if there is a better solution.

Full diff: https://github.com/llvm/llvm-project/pull/166945.diff

3 Files Affected:

(modified) llvm/lib/Transforms/InstCombine/InstructionCombining.cpp (+12)
(modified) llvm/test/Transforms/InstCombine/sink-dereferenceable-assume.ll (+4-3)
(modified) llvm/test/Transforms/PhaseOrdering/AArch64/std-find.ll (+46-56)

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index b158e0f626850..cea5be2468feb 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -5413,6 +5413,18 @@ bool InstCombinerImpl::tryToSinkInstruction(Instruction *I,
         return false;
   }
 
+  // Do not sink if there are dereferenceable assumes that would be removed.
+  for (User *User : I->users()) {
+    auto *CI = dyn_cast<CallInst>(User);
+    if (!CI || CI->getParent() == DestBlock)
+      continue;
+
+    if (CI->getIntrinsicID() == Intrinsic::assume &&
+        CI->getOperandBundle("dereferenceable")) {
+      return false;
+    }
+  }
+
   I->dropDroppableUses([&](const Use *U) {
     auto *I = dyn_cast<Instruction>(U->getUser());
     if (I && I->getParent() != DestBlock) {
diff --git a/llvm/test/Transforms/InstCombine/sink-dereferenceable-assume.ll b/llvm/test/Transforms/InstCombine/sink-dereferenceable-assume.ll
index 953132309900b..353e0bb191ed1 100644
--- a/llvm/test/Transforms/InstCombine/sink-dereferenceable-assume.ll
+++ b/llvm/test/Transforms/InstCombine/sink-dereferenceable-assume.ll
@@ -5,11 +5,12 @@ define i64 @test_sink_with_dereferenceable_assume(ptr %p, ptr %q, i1 %cond) {
 ; CHECK-LABEL: define i64 @test_sink_with_dereferenceable_assume(
 ; CHECK-SAME: ptr [[P:%.*]], ptr [[Q:%.*]], i1 [[COND:%.*]]) {
 ; CHECK-NEXT:  [[ENTRY:.*:]]
-; CHECK-NEXT:    br i1 [[COND]], label %[[THEN:.*]], label %[[ELSE:.*]]
-; CHECK:       [[THEN]]:
-; CHECK-NEXT:    [[Q_INT:%.*]] = ptrtoint ptr [[Q]] to i64
 ; CHECK-NEXT:    [[P_INT:%.*]] = ptrtoint ptr [[P]] to i64
+; CHECK-NEXT:    [[Q_INT:%.*]] = ptrtoint ptr [[Q]] to i64
 ; CHECK-NEXT:    [[DIFF:%.*]] = sub i64 [[Q_INT]], [[P_INT]]
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[P]], i64 [[DIFF]]) ]
+; CHECK-NEXT:    br i1 [[COND]], label %[[THEN:.*]], label %[[ELSE:.*]]
+; CHECK:       [[THEN]]:
 ; CHECK-NEXT:    ret i64 [[DIFF]]
 ; CHECK:       [[ELSE]]:
 ; CHECK-NEXT:    ret i64 0
diff --git a/llvm/test/Transforms/PhaseOrdering/AArch64/std-find.ll b/llvm/test/Transforms/PhaseOrdering/AArch64/std-find.ll
index 33e3e83770e7f..e9149795954ec 100644
--- a/llvm/test/Transforms/PhaseOrdering/AArch64/std-find.ll
+++ b/llvm/test/Transforms/PhaseOrdering/AArch64/std-find.ll
@@ -133,75 +133,65 @@ define ptr @std_find_caller(ptr noundef %first, ptr noundef %last) {
 ; CHECK-LABEL: define noundef ptr @std_find_caller(
 ; CHECK-SAME: ptr noundef [[FIRST:%.*]], ptr noundef [[LAST:%.*]]) local_unnamed_addr #[[ATTR0]] {
 ; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[FIRST3:%.*]] = ptrtoint ptr [[FIRST]] to i64
+; CHECK-NEXT:    [[LAST_I64:%.*]] = ptrtoint ptr [[LAST]] to i64
+; CHECK-NEXT:    [[PTR_SUB:%.*]] = sub i64 [[LAST_I64]], [[FIRST3]]
 ; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[FIRST]], i64 2) ]
 ; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "align"(ptr [[LAST]], i64 2) ]
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "dereferenceable"(ptr [[FIRST]], i64 [[PTR_SUB]]) ]
 ; CHECK-NEXT:    [[PRE_I:%.*]] = icmp eq ptr [[FIRST]], [[LAST]]
 ; CHECK-NEXT:    br i1 [[PRE_I]], label %[[STD_FIND_GENERIC_IMPL_EXIT:.*]], label %[[LOOP_HEADER_I_PREHEADER:.*]]
 ; CHECK:       [[LOOP_HEADER_I_PREHEADER]]:
-; CHECK-NEXT:    [[LAST2:%.*]] = ptrtoint ptr [[LAST]] to i64
-; CHECK-NEXT:    [[FIRST3:%.*]] = ptrtoint ptr [[FIRST]] to i64
-; CHECK-NEXT:    [[LAST_I64:%.*]] = ptrtoint ptr [[LAST]] to i64
-; CHECK-NEXT:    [[FIRST1:%.*]] = ptrtoint ptr [[FIRST]] to i64
-; CHECK-NEXT:    [[PTR_SUB:%.*]] = sub i64 [[LAST_I64]], [[FIRST1]]
 ; CHECK-NEXT:    [[SCEVGEP:%.*]] = getelementptr i8, ptr [[FIRST]], i64 [[PTR_SUB]]
-; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[LAST2]], -2
+; CHECK-NEXT:    [[TMP0:%.*]] = add i64 [[LAST_I64]], -2
 ; CHECK-NEXT:    [[TMP1:%.*]] = sub i64 [[TMP0]], [[FIRST3]]
 ; CHECK-NEXT:    [[TMP2:%.*]] = lshr exact i64 [[TMP1]], 1
 ; CHECK-NEXT:    [[TMP3:%.*]] = add nuw i64 [[TMP2]], 1
-; CHECK-NEXT:    [[XTRAITER:%.*]] = and i64 [[TMP3]], 3
-; CHECK-NEXT:    [[TMP4:%.*]] = and i64 [[TMP1]], 6
-; CHECK-NEXT:    [[LCMP_MOD_NOT:%.*]] = icmp eq i64 [[TMP4]], 6
-; CHECK-NEXT:    br i1 [[LCMP_MOD_NOT]], label %[[LOOP_HEADER_I_PROL_LOOPEXIT:.*]], label %[[LOOP_HEADER_I_PROL:.*]]
-; CHECK:       [[LOOP_HEADER_I_PROL]]:
-; CHECK-NEXT:    [[PTR_IV_I_PROL:%.*]] = phi ptr [ [[PTR_IV_NEXT_I_PROL:%.*]], %[[LOOP_LATCH_I_PROL:.*]] ], [ [[FIRST]], %[[LOOP_HEADER_I_PREHEADER]] ]
-; CHECK-NEXT:    [[PROL_ITER:%.*]] = phi i64 [ [[PROL_ITER_NEXT:%.*]], %[[LOOP_LATCH_I_PROL]] ], [ 0, %[[LOOP_HEADER_I_PREHEADER]] ]
-; CHECK-NEXT:    [[L_I_PROL:%.*]] = load i16, ptr [[PTR_IV_I_PROL]], align 2
-; CHECK-NEXT:    [[C_1_I_PROL:%.*]] = icmp eq i16 [[L_I_PROL]], 1
-; CHECK-NEXT:    br i1 [[C_1_I_PROL]], label %[[STD_FIND_GENERIC_IMPL_EXIT]], label %[[LOOP_LATCH_I_PROL]]
-; CHECK:       [[LOOP_LATCH_I_PROL]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I_PROL]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I_PROL]], i64 2
-; CHECK-NEXT:    [[PROL_ITER_NEXT]] = add i64 [[PROL_ITER]], 1
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ult i64 [[TMP1]], 158
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label %[[LOOP_HEADER_I_PREHEADER2:.*]], label %[[VECTOR_PH:.*]]
+; CHECK:       [[VECTOR_PH]]:
+; CHECK-NEXT:    [[XTRAITER:%.*]] = and i64 [[TMP3]], -8
+; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
+; CHECK:       [[VECTOR_BODY]]:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i64 [ 0, %[[VECTOR_PH]] ], [ [[PROL_ITER_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[OFFSET_IDX:%.*]] = shl i64 [[INDEX]], 1
+; CHECK-NEXT:    [[NEXT_GEP:%.*]] = getelementptr i8, ptr [[FIRST]], i64 [[OFFSET_IDX]]
+; CHECK-NEXT:    [[WIDE_LOAD:%.*]] = load <8 x i16>, ptr [[NEXT_GEP]], align 2
+; CHECK-NEXT:    [[WIDE_LOAD_FR:%.*]] = freeze <8 x i16> [[WIDE_LOAD]]
+; CHECK-NEXT:    [[TMP4:%.*]] = icmp eq <8 x i16> [[WIDE_LOAD_FR]], splat (i16 1)
+; CHECK-NEXT:    [[PROL_ITER_NEXT]] = add nuw i64 [[INDEX]], 8
+; CHECK-NEXT:    [[TMP5:%.*]] = bitcast <8 x i1> [[TMP4]] to i8
+; CHECK-NEXT:    [[TMP6:%.*]] = icmp ne i8 [[TMP5]], 0
 ; CHECK-NEXT:    [[PROL_ITER_CMP_NOT:%.*]] = icmp eq i64 [[PROL_ITER_NEXT]], [[XTRAITER]]
-; CHECK-NEXT:    br i1 [[PROL_ITER_CMP_NOT]], label %[[LOOP_HEADER_I_PROL_LOOPEXIT]], label %[[LOOP_HEADER_I_PROL]], !llvm.loop [[LOOP3:![0-9]+]]
-; CHECK:       [[LOOP_HEADER_I_PROL_LOOPEXIT]]:
-; CHECK-NEXT:    [[PTR_IV_I_UNR:%.*]] = phi ptr [ [[FIRST]], %[[LOOP_HEADER_I_PREHEADER]] ], [ [[PTR_IV_NEXT_I_PROL]], %[[LOOP_LATCH_I_PROL]] ]
-; CHECK-NEXT:    [[TMP5:%.*]] = icmp ult i64 [[TMP1]], 6
-; CHECK-NEXT:    br i1 [[TMP5]], label %[[STD_FIND_GENERIC_IMPL_EXIT]], label %[[LOOP_HEADER_I:.*]]
+; CHECK-NEXT:    [[TMP8:%.*]] = or i1 [[TMP6]], [[PROL_ITER_CMP_NOT]]
+; CHECK-NEXT:    br i1 [[TMP8]], label %[[MIDDLE_SPLIT:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK:       [[MIDDLE_SPLIT]]:
+; CHECK-NEXT:    [[TMP9:%.*]] = shl i64 [[XTRAITER]], 1
+; CHECK-NEXT:    [[TMP10:%.*]] = getelementptr i8, ptr [[FIRST]], i64 [[TMP9]]
+; CHECK-NEXT:    br i1 [[TMP6]], label %[[VECTOR_EARLY_EXIT:.*]], label %[[MIDDLE_BLOCK:.*]]
+; CHECK:       [[MIDDLE_BLOCK]]:
+; CHECK-NEXT:    [[CMP_N:%.*]] = icmp eq i64 [[TMP3]], [[XTRAITER]]
+; CHECK-NEXT:    br i1 [[CMP_N]], label %[[STD_FIND_GENERIC_IMPL_EXIT]], label %[[LOOP_HEADER_I_PREHEADER2]]
+; CHECK:       [[LOOP_HEADER_I_PREHEADER2]]:
+; CHECK-NEXT:    [[PTR_IV_I_PH:%.*]] = phi ptr [ [[FIRST]], %[[LOOP_HEADER_I_PREHEADER]] ], [ [[TMP10]], %[[MIDDLE_BLOCK]] ]
+; CHECK-NEXT:    br label %[[LOOP_HEADER_I:.*]]
+; CHECK:       [[VECTOR_EARLY_EXIT]]:
+; CHECK-NEXT:    [[TMP11:%.*]] = tail call i64 @llvm.experimental.cttz.elts.i64.v8i1(<8 x i1> [[TMP4]], i1 true)
+; CHECK-NEXT:    [[TMP12:%.*]] = add i64 [[INDEX]], [[TMP11]]
+; CHECK-NEXT:    [[TMP13:%.*]] = shl i64 [[TMP12]], 1
+; CHECK-NEXT:    [[TMP14:%.*]] = getelementptr i8, ptr [[FIRST]], i64 [[TMP13]]
+; CHECK-NEXT:    br label %[[STD_FIND_GENERIC_IMPL_EXIT]]
 ; CHECK:       [[LOOP_HEADER_I]]:
-; CHECK-NEXT:    [[PTR_IV_I:%.*]] = phi ptr [ [[PTR_IV_NEXT_I_3:%.*]], %[[LOOP_LATCH_I_3:.*]] ], [ [[PTR_IV_I_UNR]], %[[LOOP_HEADER_I_PROL_LOOPEXIT]] ]
+; CHECK-NEXT:    [[PTR_IV_I:%.*]] = phi ptr [ [[PTR_IV_NEXT_I:%.*]], %[[LOOP_LATCH_I:.*]] ], [ [[PTR_IV_I_PH]], %[[LOOP_HEADER_I_PREHEADER2]] ]
 ; CHECK-NEXT:    [[L_I:%.*]] = load i16, ptr [[PTR_IV_I]], align 2
 ; CHECK-NEXT:    [[C_1_I:%.*]] = icmp eq i16 [[L_I]], 1
-; CHECK-NEXT:    br i1 [[C_1_I]], label %[[STD_FIND_GENERIC_IMPL_EXIT]], label %[[LOOP_LATCH_I:.*]]
+; CHECK-NEXT:    br i1 [[C_1_I]], label %[[STD_FIND_GENERIC_IMPL_EXIT]], label %[[LOOP_LATCH_I]]
 ; CHECK:       [[LOOP_LATCH_I]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I:%.*]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 2
-; CHECK-NEXT:    [[L_I_1:%.*]] = load i16, ptr [[PTR_IV_NEXT_I]], align 2
-; CHECK-NEXT:    [[C_1_I_1:%.*]] = icmp eq i16 [[L_I_1]], 1
-; CHECK-NEXT:    br i1 [[C_1_I_1]], label %[[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT11:.*]], label %[[LOOP_LATCH_I_1:.*]]
-; CHECK:       [[LOOP_LATCH_I_1]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I_1:%.*]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 4
-; CHECK-NEXT:    [[L_I_2:%.*]] = load i16, ptr [[PTR_IV_NEXT_I_1]], align 2
-; CHECK-NEXT:    [[C_1_I_2:%.*]] = icmp eq i16 [[L_I_2]], 1
-; CHECK-NEXT:    br i1 [[C_1_I_2]], label %[[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT9:.*]], label %[[LOOP_LATCH_I_2:.*]]
-; CHECK:       [[LOOP_LATCH_I_2]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I_2:%.*]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 6
-; CHECK-NEXT:    [[L_I_3:%.*]] = load i16, ptr [[PTR_IV_NEXT_I_2]], align 2
-; CHECK-NEXT:    [[C_1_I_3:%.*]] = icmp eq i16 [[L_I_3]], 1
-; CHECK-NEXT:    br i1 [[C_1_I_3]], label %[[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT7:.*]], label %[[LOOP_LATCH_I_3]]
-; CHECK:       [[LOOP_LATCH_I_3]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I_3]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 8
-; CHECK-NEXT:    [[EC_I_3:%.*]] = icmp eq ptr [[PTR_IV_NEXT_I_3]], [[LAST]]
-; CHECK-NEXT:    br i1 [[EC_I_3]], label %[[STD_FIND_GENERIC_IMPL_EXIT]], label %[[LOOP_HEADER_I]]
-; CHECK:       [[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT7]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I_2_LE:%.*]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 6
-; CHECK-NEXT:    br label %[[STD_FIND_GENERIC_IMPL_EXIT]]
-; CHECK:       [[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT9]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I_1_LE:%.*]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 4
-; CHECK-NEXT:    br label %[[STD_FIND_GENERIC_IMPL_EXIT]]
-; CHECK:       [[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT11]]:
-; CHECK-NEXT:    [[PTR_IV_NEXT_I_LE:%.*]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 2
-; CHECK-NEXT:    br label %[[STD_FIND_GENERIC_IMPL_EXIT]]
+; CHECK-NEXT:    [[PTR_IV_NEXT_I]] = getelementptr inbounds nuw i8, ptr [[PTR_IV_I]], i64 2
+; CHECK-NEXT:    [[EC_I:%.*]] = icmp eq ptr [[PTR_IV_NEXT_I]], [[LAST]]
+; CHECK-NEXT:    br i1 [[EC_I]], label %[[STD_FIND_GENERIC_IMPL_EXIT]], label %[[LOOP_HEADER_I]], !llvm.loop [[LOOP4:![0-9]+]]
 ; CHECK:       [[STD_FIND_GENERIC_IMPL_EXIT]]:
-; CHECK-NEXT:    [[RES_I:%.*]] = phi ptr [ [[FIRST]], %[[ENTRY]] ], [ [[SCEVGEP]], %[[LOOP_HEADER_I_PROL_LOOPEXIT]] ], [ [[PTR_IV_NEXT_I_2_LE]], %[[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT7]] ], [ [[PTR_IV_NEXT_I_1_LE]], %[[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT9]] ], [ [[PTR_IV_NEXT_I_LE]], %[[STD_FIND_GENERIC_IMPL_EXIT_LOOPEXIT_UNR_LCSSA_LOOPEXIT_SPLIT_LOOP_EXIT11]] ], [ [[SCEVGEP]], %[[LOOP_LATCH_I_3]] ], [ [[PTR_IV_I]], %[[LOOP_HEADER_I]] ], [ [[PTR_IV_I_PROL]], %[[LOOP_HEADER_I_PROL]] ]
+; CHECK-NEXT:    [[RES_I:%.*]] = phi ptr [ [[FIRST]], %[[ENTRY]] ], [ [[SCEVGEP]], %[[MIDDLE_BLOCK]] ], [ [[TMP14]], %[[VECTOR_EARLY_EXIT]] ], [ [[SCEVGEP]], %[[LOOP_LATCH_I]] ], [ [[PTR_IV_I]], %[[LOOP_HEADER_I]] ]
 ; CHECK-NEXT:    ret ptr [[RES_I]]
 ;
 entry:
@@ -241,6 +231,6 @@ declare void @llvm.assume(i1 noundef)
 ; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]], [[META2:![0-9]+]]}
 ; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
 ; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
-; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META4:![0-9]+]]}
-; CHECK: [[META4]] = !{!"llvm.loop.unroll.disable"}
+; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META1]], [[META2]]}
+; CHECK: [[LOOP4]] = distinct !{[[LOOP4]], [[META2]], [[META1]]}
 ;.

dtcxzyw · 2025-11-07T15:49:08Z

llvm/lib/Transforms/InstCombine/InstructionCombining.cpp

  }

+  // Do not sink if there are dereferenceable assumes that would be removed.
+  for (User *User : I->users()) {


Can we bail out this case in getOptionalSinkBlockForInst?

Yep thanks, we can do better in getOptionalSinkBlockForInst, by just not skipping such assumes there we can still sink up to the deref assume. Also added some extra tests.

Did you forget to push the changes?

Ah yes, sorry about that. Should be pushed now

Currently sinking assumes in instcombine drops assumes if they would prevent sinking. Removing dereferenceable assumptions earlier on can inhibit vectorization of early-exit loops in practice. Special-case deferenceable assumptions so that they block sinking. This can be combined with a separate change to drop dereferencebale assumptions after vectorization: https://clang.godbolt.org/z/jGqcx3sbs Not sure if there is a better solution.

dtcxzyw

LGTM.

…f assumptions. (#166945) Currently sinking assumes in instcombine drops assumes if they would prevent sinking. Removing dereferenceable assumptions earlier on can inhibit vectorization of early-exit loops in practice. Special-case deferenceable assumptions so that they block sinking. This can be combined with a separate change to drop dereferencebale assumptions after vectorization: https://clang.godbolt.org/z/jGqcx3sbs PR: llvm/llvm-project#166945

…166947) This patch adds another run of DropUnnecessaryAssumes after vectorization, to clean up assumes that are not longer needed after this point. The main example of such an assume is currently dereferenceable assumptions. This complements #166945, which avoids sinking code if it would mean remove a dereferenceable assumption. There are a few additional cases where some unneeded assumes are left over after vectorization that also get cleaned up. The main motivation is to work together with #166945, but there may be a better solution. Adding another instance of this pass to the pipeline is not great, but compile-time impact seems in the noise: https://llvm-compile-time-tracker.com/compare.php?from=55e71fe08b6406ec7ce2c81ce042e48717acf204&to=85da4ee3a74126f557cdc74c7b40e048dacb3fc4&stat=instructions:u PR: #166947

…rization. (#166947) This patch adds another run of DropUnnecessaryAssumes after vectorization, to clean up assumes that are not longer needed after this point. The main example of such an assume is currently dereferenceable assumptions. This complements llvm/llvm-project#166945, which avoids sinking code if it would mean remove a dereferenceable assumption. There are a few additional cases where some unneeded assumes are left over after vectorization that also get cleaned up. The main motivation is to work together with llvm/llvm-project#166945, but there may be a better solution. Adding another instance of this pass to the pipeline is not great, but compile-time impact seems in the noise: https://llvm-compile-time-tracker.com/compare.php?from=55e71fe08b6406ec7ce2c81ce042e48717acf204&to=85da4ee3a74126f557cdc74c7b40e048dacb3fc4&stat=instructions:u PR: llvm/llvm-project#166947

…ns. (llvm#166945) Currently sinking assumes in instcombine drops assumes if they would prevent sinking. Removing dereferenceable assumptions earlier on can inhibit vectorization of early-exit loops in practice. Special-case deferenceable assumptions so that they block sinking. This can be combined with a separate change to drop dereferencebale assumptions after vectorization: https://clang.godbolt.org/z/jGqcx3sbs PR: llvm#166945 (cherry picked from commit 700b77b)

fhahn requested review from antoniofrighetto, dtcxzyw, goldsteinn and nikic November 7, 2025 14:43

llvmbot added llvm:instcombine Covers the InstCombine, InstSimplify and AggressiveInstCombine passes llvm:transforms labels Nov 7, 2025

fhahn mentioned this pull request Nov 7, 2025

[DropAssumes] Drop dereferenceable assumptions after vectorization. #166947

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dtcxzyw reviewed Nov 7, 2025

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fhahn added 3 commits November 8, 2025 14:52

[InstCombine] Add extra tests.

bff824e

!fixup move code to getOptionalSinkBlockForInst.

ae29bfe

fhahn force-pushed the ic-sinking-with-deref-assumptions branch from cdcf6e8 to ae29bfe Compare November 8, 2025 14:54

dtcxzyw approved these changes Nov 8, 2025

View reviewed changes

Merge branch 'main' into ic-sinking-with-deref-assumptions

2f5e3de

fhahn enabled auto-merge (squash) November 9, 2025 20:40

fhahn merged commit 700b77b into llvm:main Nov 9, 2025
9 of 10 checks passed

fhahn deleted the ic-sinking-with-deref-assumptions branch November 9, 2025 21:23

nigham mentioned this pull request Nov 10, 2025

[libc] Implement fchown #167286

Merged

fhahn mentioned this pull request Nov 10, 2025

[InstCombine] Don't sink if it would require dropping deref assumptio… swiftlang/llvm-project#11784

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[InstCombine] Don't sink if it would require dropping deref assumptions. #166945

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