[CVP] Use at-use info in processBinOp

[dtcxzyw]

This patch uses getConstantRangeAtUse to infer nsw/nuw flags with at-use info. It will enables more optimizations in InstCombine.

Compile-time impact: http://llvm-compile-time-tracker.com/compare.php?from=a5ed14bc8e122fa5ac0aa81f8d8390931bd6b4e4&to=a83d3402b663439b91cb37a046fb7ac0220ba5c7&stat=instructions%3Au

Related issue: #87854

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

Changes

This patch uses getConstantRangeAtUse to infer nsw/nuw flags with at-use info. It will enables more optimizations in InstCombine.

Compile-time impact: http://llvm-compile-time-tracker.com/compare.php?from=a5ed14bc8e122fa5ac0aa81f8d8390931bd6b4e4&to=a83d3402b663439b91cb37a046fb7ac0220ba5c7&stat=instructions%3Au

Related issue: #87854

---

Full diff: https://github.com/llvm/llvm-project/pull/88523.diff

3 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp (+4-7)
• (modified) llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll (+34)
• (modified) llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll (+2-1)

diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index fb334e8292eb18..715cdaff972796 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -1105,13 +1105,10 @@ static bool processBinOp(BinaryOperator *BinOp, LazyValueInfo *LVI) {
     return false;
 
   Instruction::BinaryOps Opcode = BinOp->getOpcode();
-  Value *LHS = BinOp->getOperand(0);
-  Value *RHS = BinOp->getOperand(1);
-
-  ConstantRange LRange =
-      LVI->getConstantRange(LHS, BinOp, /*UndefAllowed*/ false);
-  ConstantRange RRange =
-      LVI->getConstantRange(RHS, BinOp, /*UndefAllowed*/ false);
+  ConstantRange LRange = LVI->getConstantRangeAtUse(BinOp->getOperandUse(0),
+                                                    /*UndefAllowed=*/false);
+  ConstantRange RRange = LVI->getConstantRangeAtUse(BinOp->getOperandUse(1),
+                                                    /*UndefAllowed=*/false);
 
   bool Changed = false;
   bool NewNUW = false, NewNSW = false;
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll b/llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll
index 0b95139f3dcbaa..3af4c70a5621c8 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/cond-at-use.ll
@@ -596,3 +596,37 @@ define i16 @and_elide_poison_flags_missing_noundef(i16 %a) {
   %sel = select i1 %cmp, i16 %and, i16 24
   ret i16 %sel
 }
+
+define i32 @pr87854(i32 noundef %x.1, i32 noundef %i) {
+; CHECK-LABEL: @pr87854(
+; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[X_1:%.*]], -1
+; CHECK-NEXT:    tail call void @llvm.assume(i1 [[COND]])
+; CHECK-NEXT:    [[INBOUNDS:%.*]] = icmp ult i32 [[I:%.*]], [[X_1]]
+; CHECK-NEXT:    [[NEXT:%.*]] = add nuw i32 [[I]], 1
+; CHECK-NEXT:    [[SPEC_SELECT:%.*]] = select i1 [[INBOUNDS]], i32 [[NEXT]], i32 -1
+; CHECK-NEXT:    ret i32 [[SPEC_SELECT]]
+;
+  %cond = icmp sgt i32 %x.1, -1
+  tail call void @llvm.assume(i1 %cond)
+  %inbounds = icmp ult i32 %i, %x.1
+  %next = add i32 %i, 1
+  %spec.select = select i1 %inbounds, i32 %next, i32 -1
+  ret i32 %spec.select
+}
+
+define i64 @test_shl_nsw_at_use(i64 noundef %x) {
+; CHECK-LABEL: @test_shl_nsw_at_use(
+; CHECK-NEXT:    [[ADD:%.*]] = add i64 [[X:%.*]], 2147483648
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult i64 [[ADD]], 4294967296
+; CHECK-NEXT:    [[SHL:%.*]] = shl nsw i64 [[X]], 32
+; CHECK-NEXT:    [[SHR:%.*]] = ashr exact i64 [[SHL]], 32
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[CMP]], i64 [[SHR]], i64 0
+; CHECK-NEXT:    ret i64 [[RES]]
+;
+  %add = add i64 %x, 2147483648
+  %cmp = icmp ult i64 %add, 4294967296
+  %shl = shl i64 %x, 32
+  %shr = ashr exact i64 %shl, 32
+  %res = select i1 %cmp, i64 %shr, i64 0
+  ret i64 %res
+}
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll b/llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll
index 7f102bc1e4fe2e..7e712947e37ad9 100644
--- a/llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/phi-common-val.ll
@@ -156,12 +156,13 @@ bb3:
 define i32 @PR43802_without_nowrap(i32 %arg) {
 ; CHECK-LABEL: @PR43802_without_nowrap(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[SUB:%.*]] = sub i32 0, [[ARG:%.*]]
+; CHECK-NEXT:    [[SUB1:%.*]] = sub nsw i32 0, [[ARG:%.*]]
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[ARG]], -2147483648
 ; CHECK-NEXT:    br i1 [[CMP]], label [[BB2:%.*]], label [[BB3:%.*]]
 ; CHECK:       bb2:
 ; CHECK-NEXT:    br label [[BB3]]
 ; CHECK:       bb3:
+; CHECK-NEXT:    [[SUB:%.*]] = phi i32 [ -2147483648, [[BB2]] ], [ [[SUB1]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    ret i32 [[SUB]]
 ;
 entry:

[dtcxzyw]

I don't know why the nsw flag cannot be inferred from the assumption. intersectAssumeOrGuardBlockValueConstantRange should handle this case.

[goldsteinn]

I don't think intersectAssumeOrGuardBlockValueConstantRange should be the one getting the nsw, its the select that enables it.
but either way, I think the issue is that UseBlockValue is false so we don't actually compute the %x.1 CR when evaluating the inbounds cmp.

[goldsteinn]

As an aside, we may want to test increasing const unsigned MaxUsesToInspect = 3;. Seems startlingly.

[nikic]

I think the issue is that UseBlockValue is false so we don't actually compute the %x.1 CR when evaluating the inbounds cmp.

Yes, we don't use block values when deriving information from select conditions right now. I'm not sure doing this is viable, especially in the at-use logic.

[dtcxzyw]

It will be folded by instcombine later: https://godbolt.org/z/4MGsvnsnT

[goldsteinn]

LGTM. Wait on another.

[nikic]

LGTM

[XChy]

Thanks. Looks like we have replaced all getConstantRange with getConstantRangeAtUse in CVP.