[llvm] r371101 - [InstCombine] foldICmpBinOp(): consider inverted check in 'unsigned sub overflow' check
Roman Lebedev via llvm-commits
llvm-commits at lists.llvm.org
Thu Sep 5 10:41:02 PDT 2019
Author: lebedevri
Date: Thu Sep 5 10:41:02 2019
New Revision: 371101
URL: http://llvm.org/viewvc/llvm-project?rev=371101&view=rev
Log:
[InstCombine] foldICmpBinOp(): consider inverted check in 'unsigned sub overflow' check
A follow-up for r329011.
This may be changed to produce @llvm.sub.with.overflow in a later patch,
but for now just make things more consistent overall.
A few observations stem from this:
* There does not seem to be a similar one-instruction fold for uadd-overflow
* I'm not sure we'll want to canonicalize `B u> A` as `usub.with.overflow`,
so since the `icmp` here no longer refers to `sub`,
reconstructing `usub.with.overflow` will be problematic,
and will likely require standalone pass (similar to DivRemPairs).
https://rise4fun.com/Alive/Zqs
Name: (A - B) u> A --> B u> A
%t0 = sub i8 %A, %B
%r = icmp ugt i8 %t0, %A
=>
%r = icmp ugt i8 %B, %A
Name: (A - B) u<= A --> B u<= A
%t0 = sub i8 %A, %B
%r = icmp ule i8 %t0, %A
=>
%r = icmp ule i8 %B, %A
Name: C u< (C - D) --> C u< D
%t0 = sub i8 %C, %D
%r = icmp ult i8 %C, %t0
=>
%r = icmp ult i8 %C, %D
Name: C u>= (C - D) --> C u>= D
%t0 = sub i8 %C, %D
%r = icmp uge i8 %C, %t0
=>
%r = icmp uge i8 %C, %D
Modified:
llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
llvm/trunk/test/Transforms/InstCombine/unsigned-sub-lack-of-overflow-check.ll
llvm/trunk/test/Transforms/InstCombine/unsigned-sub-overflow-check.ll
Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=371101&r1=371100&r2=371101&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Thu Sep 5 10:41:02 2019
@@ -3791,12 +3791,13 @@ Instruction *InstCombiner::foldICmpBinOp
if (C == Op0 && NoOp1WrapProblem)
return new ICmpInst(Pred, D, Constant::getNullValue(Op0->getType()));
- // (A - B) >u A --> A <u B
- if (A == Op1 && Pred == ICmpInst::ICMP_UGT)
- return new ICmpInst(ICmpInst::ICMP_ULT, A, B);
- // C <u (C - D) --> C <u D
- if (C == Op0 && Pred == ICmpInst::ICMP_ULT)
- return new ICmpInst(ICmpInst::ICMP_ULT, C, D);
+ // Convert sub-with-unsigned-overflow comparisons into a comparison of args.
+ // (A - B) u>/u<= A --> B u>/u<= A
+ if (A == Op1 && (Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_ULE))
+ return new ICmpInst(Pred, B, A);
+ // C u</u>= (C - D) --> C u</u>= D
+ if (C == Op0 && (Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_UGE))
+ return new ICmpInst(Pred, C, D);
// icmp (Y-X), (Z-X) -> icmp Y, Z for equalities or if there is no overflow.
if (B && D && B == D && NoOp0WrapProblem && NoOp1WrapProblem &&
Modified: llvm/trunk/test/Transforms/InstCombine/unsigned-sub-lack-of-overflow-check.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/unsigned-sub-lack-of-overflow-check.ll?rev=371101&r1=371100&r2=371101&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/unsigned-sub-lack-of-overflow-check.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/unsigned-sub-lack-of-overflow-check.ll Thu Sep 5 10:41:02 2019
@@ -8,8 +8,7 @@
define i1 @t0_basic(i8 %x, i8 %y) {
; CHECK-LABEL: @t0_basic(
-; CHECK-NEXT: [[T0:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[R:%.*]] = icmp ule i8 [[T0]], [[X]]
+; CHECK-NEXT: [[R:%.*]] = icmp ule i8 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[R]]
;
%t0 = sub i8 %x, %y
@@ -19,8 +18,7 @@ define i1 @t0_basic(i8 %x, i8 %y) {
define <2 x i1> @t1_vec(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @t1_vec(
-; CHECK-NEXT: [[T0:%.*]] = sub <2 x i8> [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[R:%.*]] = icmp ule <2 x i8> [[T0]], [[X]]
+; CHECK-NEXT: [[R:%.*]] = icmp ule <2 x i8> [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret <2 x i1> [[R]]
;
%t0 = sub <2 x i8> %x, %y
@@ -32,8 +30,7 @@ define <2 x i1> @t1_vec(<2 x i8> %x, <2
define i1 @t2_commutative(i8 %x, i8 %y) {
; CHECK-LABEL: @t2_commutative(
-; CHECK-NEXT: [[T0:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT: [[R:%.*]] = icmp ule i8 [[T0]], [[X]]
+; CHECK-NEXT: [[R:%.*]] = icmp ule i8 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[R]]
;
%t0 = sub i8 %x, %y
@@ -49,7 +46,7 @@ define i1 @t3_extrause0(i8 %x, i8 %y) {
; CHECK-LABEL: @t3_extrause0(
; CHECK-NEXT: [[T0:%.*]] = sub i8 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: call void @use8(i8 [[T0]])
-; CHECK-NEXT: [[R:%.*]] = icmp ule i8 [[T0]], [[X]]
+; CHECK-NEXT: [[R:%.*]] = icmp uge i8 [[X]], [[Y]]
; CHECK-NEXT: ret i1 [[R]]
;
%t0 = sub i8 %x, %y
Modified: llvm/trunk/test/Transforms/InstCombine/unsigned-sub-overflow-check.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/unsigned-sub-overflow-check.ll?rev=371101&r1=371100&r2=371101&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/unsigned-sub-overflow-check.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/unsigned-sub-overflow-check.ll Thu Sep 5 10:41:02 2019
@@ -8,7 +8,7 @@
define i1 @t0_basic(i8 %x, i8 %y) {
; CHECK-LABEL: @t0_basic(
-; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[R]]
;
%t0 = sub i8 %x, %y
@@ -18,7 +18,7 @@ define i1 @t0_basic(i8 %x, i8 %y) {
define <2 x i1> @t1_vec(<2 x i8> %x, <2 x i8> %y) {
; CHECK-LABEL: @t1_vec(
-; CHECK-NEXT: [[R:%.*]] = icmp ult <2 x i8> [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[R:%.*]] = icmp ugt <2 x i8> [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret <2 x i1> [[R]]
;
%t0 = sub <2 x i8> %x, %y
@@ -30,7 +30,7 @@ define <2 x i1> @t1_vec(<2 x i8> %x, <2
define i1 @t2_commutative(i8 %x, i8 %y) {
; CHECK-LABEL: @t2_commutative(
-; CHECK-NEXT: [[R:%.*]] = icmp ult i8 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: [[R:%.*]] = icmp ugt i8 [[Y:%.*]], [[X:%.*]]
; CHECK-NEXT: ret i1 [[R]]
;
%t0 = sub i8 %x, %y
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