[SCEV] Collect guard info for ICMP NE w/o constants. #160500
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@llvm/pr-subscribers-llvm-transforms @llvm/pr-subscribers-llvm-analysis Author: Florian Hahn (fhahn) ChangesWhen collecting information from loop guards, use UMax(1, %b - %a) for ICMP NE %a, %b, if neither are constant. This improves results in some cases, and will be even more useful together with
https://alive2.llvm.org/ce/z/YyBvoT Full diff: https://github.com/llvm/llvm-project/pull/160500.diff 4 Files Affected:
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index b08399b381f34..d9f14bbceeffd 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -15866,6 +15866,16 @@ void ScalarEvolution::LoopGuards::collectFromBlock(
const SCEV *OneAlignedUp =
DividesBy ? GetNextSCEVDividesByDivisor(One, DividesBy) : One;
To = SE.getUMaxExpr(FromRewritten, OneAlignedUp);
+ } else {
+ if (LHS->getType()->isPointerTy()) {
+ LHS = SE.getLosslessPtrToIntExpr(LHS);
+ RHS = SE.getLosslessPtrToIntExpr(RHS);
+ if (isa<SCEVCouldNotCompute>(LHS) || isa<SCEVCouldNotCompute>(RHS))
+ break;
+ }
+ From = SE.getMinusSCEV(RHS, LHS);
+ FromRewritten = From;
+ To = SE.getUMaxExpr(FromRewritten, SE.getOne(From->getType()));
}
break;
default:
diff --git a/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll b/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll
index e784d25385980..6db2f21352c49 100644
--- a/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll
+++ b/llvm/test/Analysis/ScalarEvolution/ptrtoint.ll
@@ -382,7 +382,7 @@ define void @pr46786_c26_char(ptr %arg, ptr %arg1, ptr %arg2) {
; X64-NEXT: %i9 = ptrtoint ptr %i7 to i64
; X64-NEXT: --> {(ptrtoint ptr %arg to i64),+,1}<nuw><%bb6> U: full-set S: full-set Exits: (-1 + (ptrtoint ptr %arg1 to i64)) LoopDispositions: { %bb6: Computable }
; X64-NEXT: %i10 = sub i64 %i9, %i4
-; X64-NEXT: --> {0,+,1}<nuw><%bb6> U: full-set S: full-set Exits: (-1 + (-1 * (ptrtoint ptr %arg to i64)) + (ptrtoint ptr %arg1 to i64)) LoopDispositions: { %bb6: Computable }
+; X64-NEXT: --> {0,+,1}<nuw><%bb6> U: [0,-1) S: [0,-1) Exits: (-1 + (-1 * (ptrtoint ptr %arg to i64)) + (ptrtoint ptr %arg1 to i64)) LoopDispositions: { %bb6: Computable }
; X64-NEXT: %i11 = getelementptr inbounds i8, ptr %arg2, i64 %i10
; X64-NEXT: --> {%arg2,+,1}<nw><%bb6> U: full-set S: full-set Exits: (-1 + (-1 * (ptrtoint ptr %arg to i64)) + (ptrtoint ptr %arg1 to i64) + %arg2) LoopDispositions: { %bb6: Computable }
; X64-NEXT: %i12 = load i8, ptr %i11, align 1
@@ -393,7 +393,7 @@ define void @pr46786_c26_char(ptr %arg, ptr %arg1, ptr %arg2) {
; X64-NEXT: --> {(1 + %arg),+,1}<nuw><%bb6> U: full-set S: full-set Exits: ((-1 * (ptrtoint ptr %arg to i64)) + (ptrtoint ptr %arg1 to i64) + %arg) LoopDispositions: { %bb6: Computable }
; X64-NEXT: Determining loop execution counts for: @pr46786_c26_char
; X64-NEXT: Loop %bb6: backedge-taken count is (-1 + (-1 * (ptrtoint ptr %arg to i64)) + (ptrtoint ptr %arg1 to i64))
-; X64-NEXT: Loop %bb6: constant max backedge-taken count is i64 -1
+; X64-NEXT: Loop %bb6: constant max backedge-taken count is i64 -2
; X64-NEXT: Loop %bb6: symbolic max backedge-taken count is (-1 + (-1 * (ptrtoint ptr %arg to i64)) + (ptrtoint ptr %arg1 to i64))
; X64-NEXT: Loop %bb6: Trip multiple is 1
;
@@ -406,9 +406,9 @@ define void @pr46786_c26_char(ptr %arg, ptr %arg1, ptr %arg2) {
; X32-NEXT: %i8 = load i8, ptr %i7, align 1
; X32-NEXT: --> %i8 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %bb6: Variant }
; X32-NEXT: %i9 = ptrtoint ptr %i7 to i64
-; X32-NEXT: --> {(zext i32 (ptrtoint ptr %arg to i32) to i64),+,1}<nuw><%bb6> U: [0,8589934591) S: [0,8589934591) Exits: ((zext i32 (-1 + (-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32)) to i64) + (zext i32 (ptrtoint ptr %arg to i32) to i64)) LoopDispositions: { %bb6: Computable }
+; X32-NEXT: --> {(zext i32 (ptrtoint ptr %arg to i32) to i64),+,1}<nuw><%bb6> U: [0,8589934590) S: [0,8589934590) Exits: ((zext i32 (-1 + (-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32)) to i64) + (zext i32 (ptrtoint ptr %arg to i32) to i64)) LoopDispositions: { %bb6: Computable }
; X32-NEXT: %i10 = sub i64 %i9, %i4
-; X32-NEXT: --> {0,+,1}<nuw><%bb6> U: [0,4294967296) S: [0,4294967296) Exits: (zext i32 (-1 + (-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32)) to i64) LoopDispositions: { %bb6: Computable }
+; X32-NEXT: --> {0,+,1}<nuw><%bb6> U: [0,4294967295) S: [0,4294967295) Exits: (zext i32 (-1 + (-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32)) to i64) LoopDispositions: { %bb6: Computable }
; X32-NEXT: %i11 = getelementptr inbounds i8, ptr %arg2, i64 %i10
; X32-NEXT: --> {%arg2,+,1}<%bb6> U: full-set S: full-set Exits: (-1 + (-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32) + %arg2) LoopDispositions: { %bb6: Computable }
; X32-NEXT: %i12 = load i8, ptr %i11, align 1
@@ -419,7 +419,7 @@ define void @pr46786_c26_char(ptr %arg, ptr %arg1, ptr %arg2) {
; X32-NEXT: --> {(1 + %arg),+,1}<nuw><%bb6> U: full-set S: full-set Exits: ((-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32) + %arg) LoopDispositions: { %bb6: Computable }
; X32-NEXT: Determining loop execution counts for: @pr46786_c26_char
; X32-NEXT: Loop %bb6: backedge-taken count is (-1 + (-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32))
-; X32-NEXT: Loop %bb6: constant max backedge-taken count is i32 -1
+; X32-NEXT: Loop %bb6: constant max backedge-taken count is i32 -2
; X32-NEXT: Loop %bb6: symbolic max backedge-taken count is (-1 + (-1 * (ptrtoint ptr %arg to i32)) + (ptrtoint ptr %arg1 to i32))
; X32-NEXT: Loop %bb6: Trip multiple is 1
;
diff --git a/llvm/test/Transforms/IndVarSimplify/pointer-loop-guards.ll b/llvm/test/Transforms/IndVarSimplify/pointer-loop-guards.ll
index 89b132e981899..9371fe24be05d 100644
--- a/llvm/test/Transforms/IndVarSimplify/pointer-loop-guards.ll
+++ b/llvm/test/Transforms/IndVarSimplify/pointer-loop-guards.ll
@@ -18,7 +18,7 @@ define i64 @test_ptr_compare_guard(ptr %start, ptr %end) {
; CHECK-NEXT: br i1 [[C_1]], label %[[LOOP_LATCH]], label %[[EXIT_LOOPEXIT:.*]]
; CHECK: [[LOOP_LATCH]]:
; CHECK-NEXT: [[PTR_IV_NEXT]] = getelementptr i8, ptr [[PTR_IV]], i64 1
-; CHECK-NEXT: [[I64_IV_NEXT]] = add i64 [[I64_IV]], 1
+; CHECK-NEXT: [[I64_IV_NEXT]] = add nuw i64 [[I64_IV]], 1
; CHECK-NEXT: [[C_2:%.*]] = icmp eq ptr [[PTR_IV_NEXT]], [[END]]
; CHECK-NEXT: br i1 [[C_2]], label %[[EXIT_LOOPEXIT]], label %[[LOOP_HEADER]]
; CHECK: [[EXIT_LOOPEXIT]]:
diff --git a/llvm/test/Transforms/LoopUnroll/scevunroll.ll b/llvm/test/Transforms/LoopUnroll/scevunroll.ll
index fa55eab062198..bc63f79296a30 100644
--- a/llvm/test/Transforms/LoopUnroll/scevunroll.ll
+++ b/llvm/test/Transforms/LoopUnroll/scevunroll.ll
@@ -465,8 +465,7 @@ define void @peel_int_eq_condition(i32 %start) {
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[IV:%.*]] = phi i32 [ [[IV_NEXT_PEEL]], [[ENTRY_PEEL_NEWPH]] ], [ [[IV_NEXT:%.*]], [[LOOP_LATCH:%.*]] ]
-; CHECK-NEXT: [[C_0:%.*]] = icmp eq i32 [[IV]], [[START]]
-; CHECK-NEXT: br i1 [[C_0]], label [[IF_THEN:%.*]], label [[LOOP_LATCH]]
+; CHECK-NEXT: br i1 false, label [[IF_THEN:%.*]], label [[LOOP_LATCH]]
; CHECK: if.then:
; CHECK-NEXT: call void @fn(i32 [[IV]])
; CHECK-NEXT: br label [[LOOP_LATCH]]
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This was referenced Sep 24, 2025
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✅ With the latest revision this PR passed the C/C++ code formatter. |
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IR corpus results: https://github.com/dtcxzyw/llvm-opt-benchmark/pull/2859/files |
When collecting information from loop guards, use UMax(1, %b - %a) for ICMP NE %a, %b, if neither are constant. This improves results in some cases, and will be even more useful together with * llvm#160012 * llvm#159942 https://alive2.llvm.org/ce/z/YyBvoT
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ping :) |
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When collecting information from loop guards, use UMax(1, %b - %a) for ICMP NE %a, %b, if neither are constant.
This improves results in some cases, and will be even more useful together with
https://alive2.llvm.org/ce/z/YyBvoT