[llvm] 53eede5 - [InstCombine] look through 'not' of ctlz/cttz op with 0-is-undef
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Sep 12 12:24:45 PDT 2022
Author: Sanjay Patel
Date: 2022-09-12T15:06:21-04:00
New Revision: 53eede597e8423410ec48b7c335c76f3b6c4c714
URL: https://github.com/llvm/llvm-project/commit/53eede597e8423410ec48b7c335c76f3b6c4c714
DIFF: https://github.com/llvm/llvm-project/commit/53eede597e8423410ec48b7c335c76f3b6c4c714.diff
LOG: [InstCombine] look through 'not' of ctlz/cttz op with 0-is-undef
https://alive2.llvm.org/ce/z/MNsC1S
This pattern was flagged at:
https://discourse.llvm.org/t/instcombines-select-optimizations-dont-trigger-reliably/64927
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 98cf450a95268..fc1a43535e350 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -952,8 +952,8 @@ static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
Value *CmpLHS = ICI->getOperand(0);
Value *CmpRHS = ICI->getOperand(1);
- // Check if the condition value compares a value for equality against zero.
- if (!ICI->isEquality() || !match(CmpRHS, m_Zero()))
+ // Check if the select condition compares a value for equality.
+ if (!ICI->isEquality())
return nullptr;
Value *SelectArg = FalseVal;
@@ -969,8 +969,15 @@ static Value *foldSelectCttzCtlz(ICmpInst *ICI, Value *TrueVal, Value *FalseVal,
// Check that 'Count' is a call to intrinsic cttz/ctlz. Also check that the
// input to the cttz/ctlz is used as LHS for the compare instruction.
- if (!match(Count, m_Intrinsic<Intrinsic::cttz>(m_Specific(CmpLHS))) &&
- !match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Specific(CmpLHS))))
+ Value *X;
+ if (!match(Count, m_Intrinsic<Intrinsic::cttz>(m_Value(X))) &&
+ !match(Count, m_Intrinsic<Intrinsic::ctlz>(m_Value(X))))
+ return nullptr;
+
+ // (X == 0) ? BitWidth : ctz(X)
+ // (X == -1) ? BitWidth : ctz(~X)
+ if ((X != CmpLHS || !match(CmpRHS, m_Zero())) &&
+ (!match(X, m_Not(m_Specific(CmpLHS))) || !match(CmpRHS, m_AllOnes())))
return nullptr;
IntrinsicInst *II = cast<IntrinsicInst>(Count);
diff --git a/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll b/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
index 8fe2a005806a8..4dff0ccc9400f 100644
--- a/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
+++ b/llvm/test/Transforms/InstCombine/select-cmp-cttz-ctlz.ll
@@ -287,13 +287,45 @@ define i32 @test5d(i64 %x) {
define i32 @not_op_ctlz(i64 %x) {
; CHECK-LABEL: @not_op_ctlz(
; CHECK-NEXT: [[N:%.*]] = xor i64 [[X:%.*]], -1
+; CHECK-NEXT: [[CT:%.*]] = tail call i64 @llvm.ctlz.i64(i64 [[N]], i1 false), !range [[RNG2]]
+; CHECK-NEXT: [[CAST:%.*]] = trunc i64 [[CT]] to i32
+; CHECK-NEXT: ret i32 [[CAST]]
+;
+ %n = xor i64 %x, -1
+ %ct = tail call i64 @llvm.ctlz.i64(i64 %n, i1 true)
+ %cast = trunc i64 %ct to i32
+ %tobool = icmp eq i64 %x, -1
+ %r = select i1 %tobool, i32 64, i32 %cast
+ ret i32 %r
+}
+
+define i32 @not_op_cttz(i64 %x) {
+; CHECK-LABEL: @not_op_cttz(
+; CHECK-NEXT: [[N:%.*]] = xor i64 [[X:%.*]], -1
+; CHECK-NEXT: [[CT:%.*]] = tail call i64 @llvm.cttz.i64(i64 [[N]], i1 false), !range [[RNG2]]
+; CHECK-NEXT: [[CAST:%.*]] = trunc i64 [[CT]] to i32
+; CHECK-NEXT: ret i32 [[CAST]]
+;
+ %n = xor i64 %x, -1
+ %ct = tail call i64 @llvm.cttz.i64(i64 %n, i1 true)
+ %cast = trunc i64 %ct to i32
+ %tobool = icmp eq i64 %x, -1
+ %r = select i1 %tobool, i32 64, i32 %cast
+ ret i32 %r
+}
+
+; negative test
+
+define i32 @not_op_ctlz_wrong_xor_op1(i64 %x) {
+; CHECK-LABEL: @not_op_ctlz_wrong_xor_op1(
+; CHECK-NEXT: [[N:%.*]] = xor i64 [[X:%.*]], -2
; CHECK-NEXT: [[CT:%.*]] = tail call i64 @llvm.ctlz.i64(i64 [[N]], i1 true), !range [[RNG2]]
; CHECK-NEXT: [[CAST:%.*]] = trunc i64 [[CT]] to i32
; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i64 [[X]], -1
; CHECK-NEXT: [[R:%.*]] = select i1 [[TOBOOL]], i32 64, i32 [[CAST]]
; CHECK-NEXT: ret i32 [[R]]
;
- %n = xor i64 %x, -1
+ %n = xor i64 %x, -2
%ct = tail call i64 @llvm.ctlz.i64(i64 %n, i1 true)
%cast = trunc i64 %ct to i32
%tobool = icmp eq i64 %x, -1
@@ -301,19 +333,40 @@ define i32 @not_op_ctlz(i64 %x) {
ret i32 %r
}
-define i32 @not_op_cttz(i64 %x) {
-; CHECK-LABEL: @not_op_cttz(
+; negative test
+
+define i32 @not_op_ctlz_wrong_xor_op0(i64 %x, i64 %y) {
+; CHECK-LABEL: @not_op_ctlz_wrong_xor_op0(
+; CHECK-NEXT: [[N:%.*]] = xor i64 [[Y:%.*]], -1
+; CHECK-NEXT: [[CT:%.*]] = tail call i64 @llvm.ctlz.i64(i64 [[N]], i1 true), !range [[RNG2]]
+; CHECK-NEXT: [[CAST:%.*]] = trunc i64 [[CT]] to i32
+; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i64 [[X:%.*]], -1
+; CHECK-NEXT: [[R:%.*]] = select i1 [[TOBOOL]], i32 64, i32 [[CAST]]
+; CHECK-NEXT: ret i32 [[R]]
+;
+ %n = xor i64 %y, -1
+ %ct = tail call i64 @llvm.ctlz.i64(i64 %n, i1 true)
+ %cast = trunc i64 %ct to i32
+ %tobool = icmp eq i64 %x, -1
+ %r = select i1 %tobool, i32 64, i32 %cast
+ ret i32 %r
+}
+
+; negative test
+
+define i32 @not_op_cttz_wrong_cmp(i64 %x) {
+; CHECK-LABEL: @not_op_cttz_wrong_cmp(
; CHECK-NEXT: [[N:%.*]] = xor i64 [[X:%.*]], -1
; CHECK-NEXT: [[CT:%.*]] = tail call i64 @llvm.cttz.i64(i64 [[N]], i1 true), !range [[RNG2]]
; CHECK-NEXT: [[CAST:%.*]] = trunc i64 [[CT]] to i32
-; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i64 [[X]], -1
+; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i64 [[X]], 0
; CHECK-NEXT: [[R:%.*]] = select i1 [[TOBOOL]], i32 64, i32 [[CAST]]
; CHECK-NEXT: ret i32 [[R]]
;
%n = xor i64 %x, -1
%ct = tail call i64 @llvm.cttz.i64(i64 %n, i1 true)
%cast = trunc i64 %ct to i32
- %tobool = icmp eq i64 %x, -1
+ %tobool = icmp eq i64 %x, 0
%r = select i1 %tobool, i32 64, i32 %cast
ret i32 %r
}
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