[llvm] [InstCombine] Fold minmax intrinsic using KnownBits information (PR #76242)
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Fri Dec 22 06:50:12 PST 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
@llvm/pr-subscribers-llvm-transforms
Author: Yingwei Zheng (dtcxzyw)
<details>
<summary>Changes</summary>
This patch tries to fold minmax intrinsic by using `computeConstantRangeIncludingKnownBits`.
Fixes regression in [_karatsuba_rec:cpython/Modules/_decimal/libmpdec/mpdecimal.c](https://github.com/python/cpython/blob/c31943af16f885c8cf5d5a690c25c366afdb2862/Modules/_decimal/libmpdec/mpdecimal.c#L5460-L5462), which was introduced by #<!-- -->71396.
See also https://github.com/dtcxzyw/llvm-opt-benchmark/issues/16#issuecomment-1865875756.
It is an alternative to #<!-- -->76221.
---
Full diff: https://github.com/llvm/llvm-project/pull/76242.diff
4 Files Affected:
- (modified) llvm/include/llvm/Analysis/ValueTracking.h (+5)
- (modified) llvm/lib/Analysis/ValueTracking.cpp (+4-4)
- (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+13)
- (modified) llvm/test/Transforms/InstCombine/minmax-intrinsics.ll (+63)
``````````diff
diff --git a/llvm/include/llvm/Analysis/ValueTracking.h b/llvm/include/llvm/Analysis/ValueTracking.h
index a3186e61b94adf..baa16306ebf5df 100644
--- a/llvm/include/llvm/Analysis/ValueTracking.h
+++ b/llvm/include/llvm/Analysis/ValueTracking.h
@@ -863,6 +863,11 @@ ConstantRange computeConstantRange(const Value *V, bool ForSigned,
const DominatorTree *DT = nullptr,
unsigned Depth = 0);
+/// Combine constant ranges from computeConstantRange() and computeKnownBits().
+ConstantRange
+computeConstantRangeIncludingKnownBits(const WithCache<const Value *> &V,
+ bool ForSigned, const SimplifyQuery &SQ);
+
/// Return true if this function can prove that the instruction I will
/// always transfer execution to one of its successors (including the next
/// instruction that follows within a basic block). E.g. this is not
diff --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 769d921eb1e8d1..cac2602d455f9d 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -6289,10 +6289,10 @@ static OverflowResult mapOverflowResult(ConstantRange::OverflowResult OR) {
}
/// Combine constant ranges from computeConstantRange() and computeKnownBits().
-static ConstantRange
-computeConstantRangeIncludingKnownBits(const WithCache<const Value *> &V,
- bool ForSigned,
- const SimplifyQuery &SQ) {
+ConstantRange
+llvm::computeConstantRangeIncludingKnownBits(const WithCache<const Value *> &V,
+ bool ForSigned,
+ const SimplifyQuery &SQ) {
ConstantRange CR1 =
ConstantRange::fromKnownBits(V.getKnownBits(SQ), ForSigned);
ConstantRange CR2 = computeConstantRange(V, ForSigned, SQ.IIQ.UseInstrInfo);
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index a272357fa04a41..76000270e868eb 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1796,6 +1796,19 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
if (Instruction *NewMinMax = factorizeMinMaxTree(II))
return NewMinMax;
+ // Try to fold minmax based on range information
+ ICmpInst::Predicate Pred =
+ ICmpInst::getNonStrictPredicate(MinMaxIntrinsic::getPredicate(IID));
+ bool IsSigned = MinMaxIntrinsic::isSigned(IID);
+ const auto LHS_CR = llvm::computeConstantRangeIncludingKnownBits(
+ I0, IsSigned, SQ.getWithInstruction(II));
+ const auto RHS_CR = llvm::computeConstantRangeIncludingKnownBits(
+ I1, IsSigned, SQ.getWithInstruction(II));
+ if (LHS_CR.icmp(Pred, RHS_CR))
+ return replaceInstUsesWith(*II, I0);
+ if (RHS_CR.icmp(Pred, LHS_CR))
+ return replaceInstUsesWith(*II, I1);
+
break;
}
case Intrinsic::bitreverse: {
diff --git a/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll b/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
index f3833a420ee835..500ea0aa73f741 100644
--- a/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
+++ b/llvm/test/Transforms/InstCombine/minmax-intrinsics.ll
@@ -2489,3 +2489,66 @@ define i1 @PR57986() {
%umin = call i1 @llvm.umin.i1(i1 ptrtoint (ptr @g to i1), i1 true)
ret i1 %umin
}
+
+define i8 @fold_umax_with_knownbits_info(i8 %a, i8 %b) {
+; CHECK-LABEL: @fold_umax_with_knownbits_info(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[A1:%.*]] = or i8 [[A:%.*]], 1
+; CHECK-NEXT: [[A2:%.*]] = shl i8 [[B:%.*]], 1
+; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[A1]], [[A2]]
+; CHECK-NEXT: ret i8 [[SUB]]
+;
+entry:
+ %a1 = or i8 %a, 1
+ %a2 = shl i8 %b, 1
+ %sub = sub i8 %a1, %a2
+ %val = call i8 @llvm.umax.i8(i8 %sub, i8 1)
+ ret i8 %val
+}
+
+define i8 @fold_umin_with_knownbits_info(i8 %a, i8 %b) {
+; CHECK-LABEL: @fold_umin_with_knownbits_info(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: ret i8 3
+;
+entry:
+ %a1 = or i8 %a, 3
+ %a2 = shl i8 %b, 2
+ %sub = sub i8 %a1, %a2
+ %val = call i8 @llvm.umin.i8(i8 %sub, i8 3)
+ ret i8 %val
+}
+
+define i8 @fold_umax_with_knownbits_info_fail(i8 %a, i8 %b) {
+; CHECK-LABEL: @fold_umax_with_knownbits_info_fail(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[A1:%.*]] = or i8 [[A:%.*]], 2
+; CHECK-NEXT: [[A2:%.*]] = shl i8 [[B:%.*]], 1
+; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[A1]], [[A2]]
+; CHECK-NEXT: [[VAL:%.*]] = call i8 @llvm.umax.i8(i8 [[SUB]], i8 1)
+; CHECK-NEXT: ret i8 [[VAL]]
+;
+entry:
+ %a1 = or i8 %a, 2
+ %a2 = shl i8 %b, 1
+ %sub = sub i8 %a1, %a2
+ %val = call i8 @llvm.umax.i8(i8 %sub, i8 1)
+ ret i8 %val
+}
+
+define i8 @fold_umin_with_knownbits_info_fail(i8 %a, i8 %b) {
+; CHECK-LABEL: @fold_umin_with_knownbits_info_fail(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[A1:%.*]] = or i8 [[A:%.*]], 1
+; CHECK-NEXT: [[A2:%.*]] = shl i8 [[B:%.*]], 2
+; CHECK-NEXT: [[SUB:%.*]] = sub i8 [[A1]], [[A2]]
+; CHECK-NEXT: [[VAL:%.*]] = call i8 @llvm.umin.i8(i8 [[SUB]], i8 3)
+; CHECK-NEXT: ret i8 [[VAL]]
+;
+entry:
+ %a1 = or i8 %a, 1
+ %a2 = shl i8 %b, 2
+ %sub = sub i8 %a1, %a2
+ %val = call i8 @llvm.umin.i8(i8 %sub, i8 3)
+ ret i8 %val
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/76242
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