[llvm] r324276 - [InstCombine] don't try to evaluate instructions with >1 use (revert r324014)
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 5 13:50:32 PST 2018
Author: spatel
Date: Mon Feb 5 13:50:32 2018
New Revision: 324276
URL: http://llvm.org/viewvc/llvm-project?rev=324276&view=rev
Log:
[InstCombine] don't try to evaluate instructions with >1 use (revert r324014)
This example causes a compile-time explosion:
define i16 @foo(i16 %in) {
%x = zext i16 %in to i32
%a1 = mul i32 %x, %x
%a2 = mul i32 %a1, %a1
%a3 = mul i32 %a2, %a2
%a4 = mul i32 %a3, %a3
%a5 = mul i32 %a4, %a4
%a6 = mul i32 %a5, %a5
%a7 = mul i32 %a6, %a6
%a8 = mul i32 %a7, %a7
%a9 = mul i32 %a8, %a8
%a10 = mul i32 %a9, %a9
%a11 = mul i32 %a10, %a10
%a12 = mul i32 %a11, %a11
%a13 = mul i32 %a12, %a12
%a14 = mul i32 %a13, %a13
%a15 = mul i32 %a14, %a14
%a16 = mul i32 %a15, %a15
%a17 = mul i32 %a16, %a16
%a18 = mul i32 %a17, %a17
%a19 = mul i32 %a18, %a18
%a20 = mul i32 %a19, %a19
%a21 = mul i32 %a20, %a20
%a22 = mul i32 %a21, %a21
%a23 = mul i32 %a22, %a22
%a24 = mul i32 %a23, %a23
%T = trunc i32 %a24 to i16
ret i16 %T
}
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll
llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp?rev=324276&r1=324275&r2=324276&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCasts.cpp Mon Feb 5 13:50:32 2018
@@ -185,14 +185,8 @@ Value *InstCombiner::EvaluateInDifferent
case Instruction::Shl:
case Instruction::UDiv:
case Instruction::URem: {
- Value *LHS, *RHS;
- if (I->getOperand(0) == I->getOperand(1)) {
- // Don't create an unnecessary value if the operands are repeated.
- LHS = RHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
- } else {
- LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
- RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
- }
+ Value *LHS = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
+ Value *RHS = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
Res = BinaryOperator::Create((Instruction::BinaryOps)Opc, LHS, RHS);
break;
}
@@ -326,15 +320,11 @@ static bool canNotEvaluateInType(Value *
assert(!isa<Constant>(V) && "Constant should already be handled.");
if (!isa<Instruction>(V))
return true;
- // We can't extend or shrink something that has multiple uses -- unless those
- // multiple uses are all in the same binop instruction -- doing so would
- // require duplicating the instruction which isn't profitable.
- if (!V->hasOneUse()) {
- if (!match(V->user_back(), m_BinOp()))
- return true;
- if (any_of(V->users(), [&](User *U) { return U != V->user_back(); }))
- return true;
- }
+ // We don't extend or shrink something that has multiple uses -- doing so
+ // would require duplicating the instruction which isn't profitable.
+ if (!V->hasOneUse())
+ return true;
+
return false;
}
Modified: llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll?rev=324276&r1=324275&r2=324276&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/cast-mul-select.ll Mon Feb 5 13:50:32 2018
@@ -47,11 +47,16 @@ define i8 @select2(i1 %cond, i8 %x, i8 %
ret i8 %F
}
+; The next 3 tests could be handled in instcombine, but evaluating values
+; with multiple uses may be very slow. Let some other pass deal with it.
+
define i32 @eval_trunc_multi_use_in_one_inst(i32 %x) {
; CHECK-LABEL: @eval_trunc_multi_use_in_one_inst(
-; CHECK-NEXT: [[A:%.*]] = add i32 [[X:%.*]], 15
-; CHECK-NEXT: [[M:%.*]] = mul i32 [[A]], [[A]]
-; CHECK-NEXT: ret i32 [[M]]
+; CHECK-NEXT: [[Z:%.*]] = zext i32 [[X:%.*]] to i64
+; CHECK-NEXT: [[A:%.*]] = add nuw nsw i64 [[Z]], 15
+; CHECK-NEXT: [[M:%.*]] = mul i64 [[A]], [[A]]
+; CHECK-NEXT: [[T:%.*]] = trunc i64 [[M]] to i32
+; CHECK-NEXT: ret i32 [[T]]
;
%z = zext i32 %x to i64
%a = add nsw nuw i64 %z, 15
@@ -62,9 +67,11 @@ define i32 @eval_trunc_multi_use_in_one_
define i32 @eval_zext_multi_use_in_one_inst(i32 %x) {
; CHECK-LABEL: @eval_zext_multi_use_in_one_inst(
-; CHECK-NEXT: [[A:%.*]] = and i32 [[X:%.*]], 5
-; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i32 [[A]], [[A]]
-; CHECK-NEXT: ret i32 [[M]]
+; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i16
+; CHECK-NEXT: [[A:%.*]] = and i16 [[T]], 5
+; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i16 [[A]], [[A]]
+; CHECK-NEXT: [[R:%.*]] = zext i16 [[M]] to i32
+; CHECK-NEXT: ret i32 [[R]]
;
%t = trunc i32 %x to i16
%a = and i16 %t, 5
@@ -75,10 +82,12 @@ define i32 @eval_zext_multi_use_in_one_i
define i32 @eval_sext_multi_use_in_one_inst(i32 %x) {
; CHECK-LABEL: @eval_sext_multi_use_in_one_inst(
-; CHECK-NEXT: [[A:%.*]] = and i32 [[X:%.*]], 14
-; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i32 [[A]], [[A]]
-; CHECK-NEXT: [[O:%.*]] = or i32 [[M]], -32768
-; CHECK-NEXT: ret i32 [[O]]
+; CHECK-NEXT: [[T:%.*]] = trunc i32 [[X:%.*]] to i16
+; CHECK-NEXT: [[A:%.*]] = and i16 [[T]], 14
+; CHECK-NEXT: [[M:%.*]] = mul nuw nsw i16 [[A]], [[A]]
+; CHECK-NEXT: [[O:%.*]] = or i16 [[M]], -32768
+; CHECK-NEXT: [[R:%.*]] = sext i16 [[O]] to i32
+; CHECK-NEXT: ret i32 [[R]]
;
%t = trunc i32 %x to i16
%a = and i16 %t, 14
Modified: llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll?rev=324276&r1=324275&r2=324276&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp-mul-zext.ll Mon Feb 5 13:50:32 2018
@@ -55,12 +55,13 @@ lor.end:
define void @PR33765(i8 %beth) {
; CHECK-LABEL: @PR33765(
-; CHECK-NEXT: [[CONV:%.*]] = zext i8 [[BETH:%.*]] to i16
+; CHECK-NEXT: [[CONV:%.*]] = zext i8 [[BETH:%.*]] to i32
; CHECK-NEXT: br i1 false, label [[IF_THEN9:%.*]], label [[IF_THEN9]]
; CHECK: if.then9:
-; CHECK-NEXT: [[MUL:%.*]] = mul nuw i16 [[CONV]], [[CONV]]
+; CHECK-NEXT: [[MUL:%.*]] = mul nuw nsw i32 [[CONV]], [[CONV]]
; CHECK-NEXT: [[TINKY:%.*]] = load i16, i16* @glob, align 2
-; CHECK-NEXT: [[CONV14:%.*]] = and i16 [[TINKY]], [[MUL]]
+; CHECK-NEXT: [[TMP1:%.*]] = trunc i32 [[MUL]] to i16
+; CHECK-NEXT: [[CONV14:%.*]] = and i16 [[TINKY]], [[TMP1]]
; CHECK-NEXT: store i16 [[CONV14]], i16* @glob, align 2
; CHECK-NEXT: ret void
;
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