[llvm] [ConstantValuePropagation] Fold calls to UCMP/SCMP when we know that ranges of operands do not overlap (PR #97235)
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Sun Jun 30 14:44:01 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: None (Poseydon42)
<details>
<summary>Changes</summary>
---
Full diff: https://github.com/llvm/llvm-project/pull/97235.diff
2 Files Affected:
- (modified) llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp (+26)
- (added) llvm/test/Transforms/CorrelatedValuePropagation/uscmp.ll (+118)
``````````diff
diff --git a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
index 88adeb597e755..853925bba0be1 100644
--- a/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
+++ b/llvm/lib/Transforms/Scalar/CorrelatedValuePropagation.cpp
@@ -548,6 +548,27 @@ static bool processAbsIntrinsic(IntrinsicInst *II, LazyValueInfo *LVI) {
return false;
}
+static bool processCmpIntrinsic(IntrinsicInst *II, LazyValueInfo *LVI) {
+ bool IsSigned = II->getIntrinsicID() == Intrinsic::scmp;
+ ConstantRange LHS_CR = LVI->getConstantRangeAtUse(II->getOperandUse(0),
+ /*UndefAllowed*/ false);
+ ConstantRange RHS_CR = LVI->getConstantRangeAtUse(II->getOperandUse(1),
+ /*UndefAllowed*/ false);
+
+ if (LHS_CR.icmp(IsSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT, RHS_CR)) {
+ II->replaceAllUsesWith(ConstantInt::get(II->getType(), 1));
+ II->eraseFromParent();
+ return true;
+ }
+ if (LHS_CR.icmp(IsSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT, RHS_CR)) {
+ II->replaceAllUsesWith(ConstantInt::getSigned(II->getType(), -1));
+ II->eraseFromParent();
+ return true;
+ }
+
+ return false;
+}
+
// See if this min/max intrinsic always picks it's one specific operand.
// If not, check whether we can canonicalize signed minmax into unsigned version
static bool processMinMaxIntrinsic(MinMaxIntrinsic *MM, LazyValueInfo *LVI) {
@@ -639,6 +660,11 @@ static bool processCallSite(CallBase &CB, LazyValueInfo *LVI) {
return processAbsIntrinsic(&cast<IntrinsicInst>(CB), LVI);
}
+ if (CB.getIntrinsicID() == Intrinsic::scmp ||
+ CB.getIntrinsicID() == Intrinsic::ucmp) {
+ return processCmpIntrinsic(&cast<IntrinsicInst>(CB), LVI);
+ }
+
if (auto *MM = dyn_cast<MinMaxIntrinsic>(&CB)) {
return processMinMaxIntrinsic(MM, LVI);
}
diff --git a/llvm/test/Transforms/CorrelatedValuePropagation/uscmp.ll b/llvm/test/Transforms/CorrelatedValuePropagation/uscmp.ll
new file mode 100644
index 0000000000000..7a3b815f64f12
--- /dev/null
+++ b/llvm/test/Transforms/CorrelatedValuePropagation/uscmp.ll
@@ -0,0 +1,118 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -passes=correlated-propagation -S | FileCheck %s
+
+; If nothing is known we can't change anything
+define i8 @ucmp_0(i32 %x, i32 %y) {
+ %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+define i8 @scmp_0(i32 %x, i32 %y) {
+ %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+; If we know that range of LHS < range of RHS then return -1
+define i8 @ucmp_1(i32 %x, i32 %y) {
+ ; X is within [4, 8)
+ %cond1 = icmp uge i32 %x, 4
+ call void @llvm.assume(i1 %cond1)
+ %cond2 = icmp ult i32 %x, 8
+ call void @llvm.assume(i1 %cond2)
+ ; Y is within [8, +INF)
+ %cond3 = icmp uge i32 %y, 8
+ call void @llvm.assume(i1 %cond3)
+
+ %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+define i8 @scmp_1(i32 %x, i32 %y) {
+ ; X is within [-5, 3)
+ %cond1 = icmp sge i32 %x, -5
+ call void @llvm.assume(i1 %cond1)
+ %cond2 = icmp slt i32 %x, 3
+ call void @llvm.assume(i1 %cond2)
+ ; Y is within [3, +INF)
+ %cond3 = icmp sge i32 %y, 3
+ call void @llvm.assume(i1 %cond3)
+
+ %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+; If we know that range of LHS > range of RHS then return 1
+define i8 @ucmp_2(i32 %x, i32 %y) {
+ ; X is within [4, +INF)
+ %cond1 = icmp uge i32 %x, 4
+ call void @llvm.assume(i1 %cond1)
+ ; Y is within [0, 4)
+ %cond2 = icmp ult i32 %y, 4
+ call void @llvm.assume(i1 %cond2)
+
+ %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+define i8 @scmp_2(i32 %x, i32 %y) {
+ ; X is within [4, +INF)
+ %cond1 = icmp sge i32 %x, 4
+ call void @llvm.assume(i1 %cond1)
+ ; Y is within [-INF, 4)
+ %cond2 = icmp slt i32 %y, 4
+ call void @llvm.assume(i1 %cond2)
+
+ %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+; Negative test: ranges overlap
+define i8 @ucmp_3(i32 %x, i32 %y) {
+ ; X is within [4, +INF)
+ %cond1 = icmp uge i32 %x, 4
+ call void @llvm.assume(i1 %cond1)
+ ; Y is within [0, 6)
+ %cond2 = icmp ult i32 %y, 6
+ call void @llvm.assume(i1 %cond2)
+
+ %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+define i8 @scmp_3(i32 %x, i32 %y) {
+ ; X is within [2, +INF)
+ %cond1 = icmp sge i32 %x, 2
+ call void @llvm.assume(i1 %cond1)
+ ; Y is within [-INF, 4)
+ %cond2 = icmp slt i32 %y, 4
+ call void @llvm.assume(i1 %cond2)
+
+ %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+; Negative test: mismatched signedness of range-establishing comparisons and
+; of the intrinsic
+define i8 @ucmp_4(i32 %x, i32 %y) {
+ ; X is within [4, +INF)
+ %cond1 = icmp sge i32 %x, 4
+ call void @llvm.assume(i1 %cond1)
+ ; Y is within [0, 4)
+ %cond2 = icmp slt i32 %y, 4
+ call void @llvm.assume(i1 %cond2)
+
+ %1 = call i8 @llvm.ucmp(i32 %x, i32 %y)
+ ret i8 %1
+}
+
+define i8 @scmp_4(i32 %x, i32 %y) {
+ ; X is within [4, +INF)
+ %cond1 = icmp uge i32 %x, 4
+ call void @llvm.assume(i1 %cond1)
+ ; Y is within [0, 4)
+ %cond2 = icmp ult i32 %y, 4
+ call void @llvm.assume(i1 %cond2)
+
+ %1 = call i8 @llvm.scmp(i32 %x, i32 %y)
+ ret i8 %1
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/97235
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