[llvm] acabad9 - [InstCombine] try to canonicalize icmp with trunc op into mask and cmp
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 26 14:44:55 PDT 2021
Author: Sanjay Patel
Date: 2021-10-26T17:43:28-04:00
New Revision: acabad9ff6bf13e00305d9d8621ee8eafc1f8b08
URL: https://github.com/llvm/llvm-project/commit/acabad9ff6bf13e00305d9d8621ee8eafc1f8b08
DIFF: https://github.com/llvm/llvm-project/commit/acabad9ff6bf13e00305d9d8621ee8eafc1f8b08.diff
LOG: [InstCombine] try to canonicalize icmp with trunc op into mask and cmp
The motivating test is based on:
https://llvm.org/PR52260
We have better analysis for X == 0, so try harder to form that.
Added:
Modified:
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/test/Transforms/InstCombine/icmp-trunc.ll
llvm/test/Transforms/InstCombine/signed-truncation-check.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 54d751e30ee3..a2db1bc83e76 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -4589,6 +4589,31 @@ Instruction *InstCombinerImpl::foldICmpEquality(ICmpInst &I) {
return nullptr;
}
+static Instruction *foldICmpWithTrunc(ICmpInst &ICmp,
+ InstCombiner::BuilderTy &Builder) {
+ const ICmpInst::Predicate Pred = ICmp.getPredicate();
+ Value *Op0 = ICmp.getOperand(0), *Op1 = ICmp.getOperand(1);
+
+ // Try to canonicalize trunc + compare-to-constant into a mask + cmp.
+ // The trunc masks high bits while the compare may effectively mask low bits.
+ Value *X;
+ const APInt *C;
+ if (match(Op0, m_OneUse(m_Trunc(m_Value(X)))) && match(Op1, m_Power2(C))) {
+ if (Pred == ICmpInst::ICMP_ULT) {
+ // (trunc X) u< Pow2C --> (X & MaskC) == 0
+ unsigned SrcBits = X->getType()->getScalarSizeInBits();
+ unsigned DstBits = Op0->getType()->getScalarSizeInBits();
+ APInt MaskC = APInt::getOneBitSet(SrcBits, DstBits) - C->zext(SrcBits);
+ Value *And = Builder.CreateAnd(X, MaskC);
+ Constant *Zero = ConstantInt::getNullValue(X->getType());
+ return new ICmpInst(ICmpInst::ICMP_EQ, And, Zero);
+ }
+ // TODO: Handle ugt.
+ }
+
+ return nullptr;
+}
+
static Instruction *foldICmpWithZextOrSext(ICmpInst &ICmp,
InstCombiner::BuilderTy &Builder) {
assert(isa<CastInst>(ICmp.getOperand(0)) && "Expected cast for operand 0");
@@ -4732,6 +4757,9 @@ Instruction *InstCombinerImpl::foldICmpWithCastOp(ICmpInst &ICmp) {
return new ICmpInst(ICmp.getPredicate(), Op0Src, NewOp1);
}
+ if (Instruction *R = foldICmpWithTrunc(ICmp, Builder))
+ return R;
+
return foldICmpWithZextOrSext(ICmp, Builder);
}
diff --git a/llvm/test/Transforms/InstCombine/icmp-trunc.ll b/llvm/test/Transforms/InstCombine/icmp-trunc.ll
index 7f961f2ccfaf..39ca767a6d2a 100644
--- a/llvm/test/Transforms/InstCombine/icmp-trunc.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-trunc.ll
@@ -5,8 +5,8 @@ declare void @use(i8)
define i1 @ult_2(i32 %x) {
; CHECK-LABEL: @ult_2(
-; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
-; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[T]], 2
+; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[X:%.*]], 254
+; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%t = trunc i32 %x to i8
@@ -16,8 +16,8 @@ define i1 @ult_2(i32 %x) {
define <2 x i1> @ult_16_splat(<2 x i16> %x) {
; CHECK-LABEL: @ult_16_splat(
-; CHECK-NEXT: [[T:%.*]] = trunc <2 x i16> [[X:%.*]] to <2 x i11>
-; CHECK-NEXT: [[R:%.*]] = icmp ult <2 x i11> [[T]], <i11 16, i11 16>
+; CHECK-NEXT: [[TMP1:%.*]] = and <2 x i16> [[X:%.*]], <i16 2032, i16 2032>
+; CHECK-NEXT: [[R:%.*]] = icmp eq <2 x i16> [[TMP1]], zeroinitializer
; CHECK-NEXT: ret <2 x i1> [[R]]
;
%t = trunc <2 x i16> %x to <2 x i11>
@@ -25,6 +25,8 @@ define <2 x i1> @ult_16_splat(<2 x i16> %x) {
ret <2 x i1> %r
}
+; negative test - need power-of-2 constant
+
define i1 @ult_3(i32 %x) {
; CHECK-LABEL: @ult_3(
; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
@@ -36,6 +38,8 @@ define i1 @ult_3(i32 %x) {
ret i1 %r
}
+; negative test - no extra use allowed
+
define i1 @ult_2_use(i32 %x) {
; CHECK-LABEL: @ult_2_use(
; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i8
@@ -53,12 +57,7 @@ define i1 @ult_2_use(i32 %x) {
define i1 @PR52260(i32 %x) {
; CHECK-LABEL: @PR52260(
-; CHECK-NEXT: [[IDXPROM:%.*]] = sext i32 [[X:%.*]] to i64
-; CHECK-NEXT: [[IDX:%.*]] = getelementptr inbounds [3 x i32], [3 x i32]* @a, i64 0, i64 [[IDXPROM]]
-; CHECK-NEXT: [[T1:%.*]] = load i32, i32* [[IDX]], align 4
-; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[T1]] to i8
-; CHECK-NEXT: [[TOBOOL:%.*]] = icmp ult i8 [[TMP1]], 2
-; CHECK-NEXT: ret i1 [[TOBOOL]]
+; CHECK-NEXT: ret i1 true
;
%idxprom = sext i32 %x to i64
%idx = getelementptr inbounds [3 x i32], [3 x i32]* @a, i64 0, i64 %idxprom
@@ -69,4 +68,3 @@ define i1 @PR52260(i32 %x) {
%tobool = icmp eq i8 %conv2, 0
ret i1 %tobool
}
-
diff --git a/llvm/test/Transforms/InstCombine/signed-truncation-check.ll b/llvm/test/Transforms/InstCombine/signed-truncation-check.ll
index 105e77284b93..6681d5021472 100644
--- a/llvm/test/Transforms/InstCombine/signed-truncation-check.ll
+++ b/llvm/test/Transforms/InstCombine/signed-truncation-check.ll
@@ -397,8 +397,8 @@ define i1 @positive_trunc_signbit_logical(i32 %arg) {
define i1 @positive_trunc_base(i32 %arg) {
; CHECK-LABEL: @positive_trunc_base(
-; CHECK-NEXT: [[T1:%.*]] = trunc i32 [[ARG:%.*]] to i16
-; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp ult i16 [[T1]], 128
+; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[ARG:%.*]], 65408
+; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[T5_SIMPLIFIED]]
;
%t1 = trunc i32 %arg to i16
@@ -411,8 +411,8 @@ define i1 @positive_trunc_base(i32 %arg) {
define i1 @positive_trunc_base_logical(i32 %arg) {
; CHECK-LABEL: @positive_trunc_base_logical(
-; CHECK-NEXT: [[T1:%.*]] = trunc i32 [[ARG:%.*]] to i16
-; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp ult i16 [[T1]], 128
+; CHECK-NEXT: [[TMP1:%.*]] = and i32 [[ARG:%.*]], 65408
+; CHECK-NEXT: [[T5_SIMPLIFIED:%.*]] = icmp eq i32 [[TMP1]], 0
; CHECK-NEXT: ret i1 [[T5_SIMPLIFIED]]
;
%t1 = trunc i32 %arg to i16
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