[llvm] r276341 - [InstSimplify] recognize trunc + icmp sgt/slt variants of select simplifications (PR28466)
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 21 14:26:45 PDT 2016
Author: spatel
Date: Thu Jul 21 16:26:45 2016
New Revision: 276341
URL: http://llvm.org/viewvc/llvm-project?rev=276341&view=rev
Log:
[InstSimplify] recognize trunc + icmp sgt/slt variants of select simplifications (PR28466)
rL245171 exposed a hole in InstSimplify that manifested in a strange way in PR28466:
https://llvm.org/bugs/show_bug.cgi?id=28466
It's possible to use trunc + icmp sgt/slt in place of an and + icmp eq/ne, so we need to
recognize that pattern to eliminate selects that are choosing between some value and some
bitmasked version of that value.
Note that there is significant room for improvement (refactoring) and enhancement (more
patterns, possibly in InstCombine rather than here).
Differential Revision: https://reviews.llvm.org/D22537
Modified:
llvm/trunk/lib/Analysis/InstructionSimplify.cpp
llvm/trunk/test/Transforms/InstSimplify/select.ll
Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=276341&r1=276340&r2=276341&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Thu Jul 21 16:26:45 2016
@@ -3406,6 +3406,33 @@ static Value *simplifySelectBitTest(Valu
return nullptr;
}
+/// An alternative way to test if a bit is set or not uses sgt/slt instead of
+/// eq/ne.
+static Value *simplifySelectWithFakeICmpEq(Value *CmpLHS, Value *TrueVal,
+ Value *FalseVal,
+ bool TrueWhenUnset) {
+ unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits();
+ APInt MinSignedValue;
+ Value *X;
+ if (match(CmpLHS, m_Trunc(m_Value(X))) && (X == TrueVal || X == FalseVal)) {
+ // icmp slt (trunc X), 0 <--> icmp ne (and X, C), 0
+ // icmp sgt (trunc X), -1 <--> icmp eq (and X, C), 0
+ unsigned DestSize = CmpLHS->getType()->getScalarSizeInBits();
+ MinSignedValue = APInt::getSignedMinValue(DestSize).zext(BitWidth);
+ } else {
+ // icmp slt X, 0 <--> icmp ne (and X, C), 0
+ // icmp sgt X, -1 <--> icmp eq (and X, C), 0
+ X = CmpLHS;
+ MinSignedValue = APInt::getSignedMinValue(BitWidth);
+ }
+
+ if (Value *V = simplifySelectBitTest(TrueVal, FalseVal, X, &MinSignedValue,
+ TrueWhenUnset))
+ return V;
+
+ return nullptr;
+}
+
/// Try to simplify a select instruction when its condition operand is an
/// integer comparison.
static Value *simplifySelectWithICmpCond(Value *CondVal, Value *TrueVal,
@@ -3418,9 +3445,6 @@ static Value *simplifySelectWithICmpCond
// FIXME: This code is nearly duplicated in InstCombine. Using/refactoring
// decomposeBitTestICmp() might help.
- unsigned BitWidth =
- Q.DL.getTypeSizeInBits(TrueVal->getType()->getScalarType());
- APInt MinSignedValue = APInt::getSignBit(BitWidth);
if (ICmpInst::isEquality(Pred) && match(CmpRHS, m_Zero())) {
Value *X;
const APInt *Y;
@@ -3429,12 +3453,14 @@ static Value *simplifySelectWithICmpCond
Pred == ICmpInst::ICMP_EQ))
return V;
} else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
- if (Value *V = simplifySelectBitTest(TrueVal, FalseVal, CmpLHS,
- &MinSignedValue, false))
+ // Comparing signed-less-than 0 checks if the sign bit is set.
+ if (Value *V = simplifySelectWithFakeICmpEq(CmpLHS, TrueVal, FalseVal,
+ false))
return V;
} else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
- if (Value *V = simplifySelectBitTest(TrueVal, FalseVal, CmpLHS,
- &MinSignedValue, true))
+ // Comparing signed-greater-than -1 checks if the sign bit is not set.
+ if (Value *V = simplifySelectWithFakeICmpEq(CmpLHS, TrueVal, FalseVal,
+ true))
return V;
}
Modified: llvm/trunk/test/Transforms/InstSimplify/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/select.ll?rev=276341&r1=276340&r2=276341&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/select.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/select.ll Thu Jul 21 16:26:45 2016
@@ -228,11 +228,8 @@ define i32 @select_icmp_and_8_ne_0_and_n
define i32 @select_icmp_trunc_8_ne_0_or_128(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_ne_0_or_128(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[TRUNC]], -1
; CHECK-NEXT: [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 [[OR]], i32 %x
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 [[OR]]
;
%trunc = trunc i32 %x to i8
%cmp = icmp sgt i8 %trunc, -1
@@ -243,11 +240,8 @@ define i32 @select_icmp_trunc_8_ne_0_or_
define i32 @select_icmp_trunc_8_ne_0_or_128_alt(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_ne_0_or_128_alt(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[TRUNC]], 0
; CHECK-NEXT: [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[OR]]
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 [[OR]]
;
%trunc = trunc i32 %x to i8
%cmp = icmp slt i8 %trunc, 0
@@ -258,11 +252,7 @@ define i32 @select_icmp_trunc_8_ne_0_or_
define i32 @select_icmp_trunc_8_eq_0_or_128(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_eq_0_or_128(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT: [[CMP:%.*]] = icmp slt i8 [[TRUNC]], 0
-; CHECK-NEXT: [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 [[OR]], i32 %x
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 %x
;
%trunc = trunc i32 %x to i8
%cmp = icmp slt i8 %trunc, 0
@@ -273,11 +263,7 @@ define i32 @select_icmp_trunc_8_eq_0_or_
define i32 @select_icmp_trunc_8_eq_0_or_128_alt(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_eq_0_or_128_alt(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i8
-; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i8 [[TRUNC]], -1
-; CHECK-NEXT: [[OR:%.*]] = or i32 %x, 128
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[OR]]
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 %x
;
%trunc = trunc i32 %x to i8
%cmp = icmp sgt i8 %trunc, -1
@@ -288,11 +274,8 @@ define i32 @select_icmp_trunc_8_eq_0_or_
define i32 @select_icmp_trunc_8_eq_0_and_not_8(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_eq_0_and_not_8(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i4 [[TRUNC]], -1
; CHECK-NEXT: [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[AND]]
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 [[AND]]
;
%trunc = trunc i32 %x to i4
%cmp = icmp sgt i4 %trunc, -1
@@ -303,11 +286,8 @@ define i32 @select_icmp_trunc_8_eq_0_and
define i32 @select_icmp_trunc_8_eq_0_and_not_8_alt(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_eq_0_and_not_8_alt(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT: [[CMP:%.*]] = icmp slt i4 [[TRUNC]], 0
; CHECK-NEXT: [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 [[AND]], i32 %x
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 [[AND]]
;
%trunc = trunc i32 %x to i4
%cmp = icmp slt i4 %trunc, 0
@@ -318,11 +298,7 @@ define i32 @select_icmp_trunc_8_eq_0_and
define i32 @select_icmp_trunc_8_ne_0_and_not_8(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_ne_0_and_not_8(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT: [[CMP:%.*]] = icmp slt i4 [[TRUNC]], 0
-; CHECK-NEXT: [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 %x, i32 [[AND]]
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 %x
;
%trunc = trunc i32 %x to i4
%cmp = icmp slt i4 %trunc, 0
@@ -333,11 +309,7 @@ define i32 @select_icmp_trunc_8_ne_0_and
define i32 @select_icmp_trunc_8_ne_0_and_not_8_alt(i32 %x) {
; CHECK-LABEL: @select_icmp_trunc_8_ne_0_and_not_8_alt(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc i32 %x to i4
-; CHECK-NEXT: [[CMP:%.*]] = icmp sgt i4 [[TRUNC]], -1
-; CHECK-NEXT: [[AND:%.*]] = and i32 %x, -9
-; CHECK-NEXT: [[SEL:%.*]] = select i1 [[CMP]], i32 [[AND]], i32 %x
-; CHECK-NEXT: ret i32 [[SEL]]
+; CHECK-NEXT: ret i32 %x
;
%trunc = trunc i32 %x to i4
%cmp = icmp sgt i4 %trunc, -1
@@ -361,11 +333,7 @@ define <2 x i32> @select_icmp_and_8_ne_0
define <2 x i32> @select_icmp_trunc_8_ne_0_and_not_8_alt_vec(<2 x i32> %x) {
; CHECK-LABEL: @select_icmp_trunc_8_ne_0_and_not_8_alt_vec(
-; CHECK-NEXT: [[TRUNC:%.*]] = trunc <2 x i32> %x to <2 x i4>
-; CHECK-NEXT: [[CMP:%.*]] = icmp sgt <2 x i4> [[TRUNC]], <i4 -1, i4 -1>
-; CHECK-NEXT: [[AND:%.*]] = and <2 x i32> %x, <i32 -9, i32 -9>
-; CHECK-NEXT: [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i32> [[AND]], <2 x i32> %x
-; CHECK-NEXT: ret <2 x i32> [[SEL]]
+; CHECK-NEXT: ret <2 x i32> %x
;
%trunc = trunc <2 x i32> %x to <2 x i4>
%cmp = icmp sgt <2 x i4> %trunc, <i4 -1, i4 -1>
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