[llvm] r321936 - [InstCombine] relax use constraint for min/max (~a, ~b) --> ~min/max(a, b)

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Sat Jan  6 09:34:22 2018
New Revision: 321936

URL: http://llvm.org/viewvc/llvm-project?rev=321936&view=rev
Log:
[InstCombine] relax use constraint for min/max (~a, ~b) --> ~min/max(a, b)

In the minimal case, this won't remove instructions, but it still improves
uses of existing values.

In the motivating example from PR35834, it does remove instructions, and
sets that case up to be optimized by something like D41603:
https://reviews.llvm.org/D41603

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/trunk/test/Transforms/InstCombine/max-of-nots.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp?rev=321936&r1=321935&r2=321936&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Sat Jan  6 09:34:22 2018
@@ -1555,8 +1555,8 @@ Instruction *InstCombiner::visitSelectIn
       // MAX(~a, ~b) -> ~MIN(a, b)
       // MIN(~a, ~b) -> ~MAX(a, b)
       Value *A, *B;
-      if (match(LHS, m_Not(m_Value(A))) && LHS->getNumUses() <= 2 &&
-          match(RHS, m_Not(m_Value(B))) && RHS->getNumUses() <= 2) {
+      if (match(LHS, m_Not(m_Value(A))) && match(RHS, m_Not(m_Value(B))) &&
+          (LHS->getNumUses() <= 2 || RHS->getNumUses() <= 2)) {
         CmpInst::Predicate InvertedPred =
             getCmpPredicateForMinMax(getInverseMinMaxSelectPattern(SPF));
         Value *InvertedCmp = Builder.CreateICmp(InvertedPred, A, B);

Modified: llvm/trunk/test/Transforms/InstCombine/max-of-nots.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/max-of-nots.ll?rev=321936&r1=321935&r2=321936&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/max-of-nots.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/max-of-nots.ll Sat Jan  6 09:34:22 2018
@@ -47,9 +47,9 @@ declare void @extra_use(i8)
 define i8 @umin_not_1_extra_use(i8 %x, i8 %y) {
 ; CHECK-LABEL: @umin_not_1_extra_use(
 ; CHECK-NEXT:    [[NX:%.*]] = xor i8 %x, -1
-; CHECK-NEXT:    [[NY:%.*]] = xor i8 %y, -1
-; CHECK-NEXT:    [[CMPXY:%.*]] = icmp ult i8 [[NX]], [[NY]]
-; CHECK-NEXT:    [[MINXY:%.*]] = select i1 [[CMPXY]], i8 [[NX]], i8 [[NY]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt i8 %x, %y
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i8 %x, i8 %y
+; CHECK-NEXT:    [[MINXY:%.*]] = xor i8 [[TMP2]], -1
 ; CHECK-NEXT:    call void @extra_use(i8 [[NX]])
 ; CHECK-NEXT:    ret i8 [[MINXY]]
 ;
@@ -84,15 +84,13 @@ define i8 @umin_not_2_extra_use(i8 %x, i
 
 define i8 @umin3_not(i8 %x, i8 %y, i8 %z) {
 ; CHECK-LABEL: @umin3_not(
-; CHECK-NEXT:    [[NX:%.*]] = xor i8 %x, -1
-; CHECK-NEXT:    [[NY:%.*]] = xor i8 %y, -1
-; CHECK-NEXT:    [[NZ:%.*]] = xor i8 %z, -1
 ; CHECK-NEXT:    [[CMPYX:%.*]] = icmp ult i8 %y, %x
-; CHECK-NEXT:    [[CMPXZ:%.*]] = icmp ult i8 [[NX]], [[NZ]]
-; CHECK-NEXT:    [[MINXZ:%.*]] = select i1 [[CMPXZ]], i8 [[NX]], i8 [[NZ]]
-; CHECK-NEXT:    [[CMPYZ:%.*]] = icmp ult i8 [[NY]], [[NZ]]
-; CHECK-NEXT:    [[MINYZ:%.*]] = select i1 [[CMPYZ]], i8 [[NY]], i8 [[NZ]]
-; CHECK-NEXT:    [[R:%.*]] = select i1 [[CMPYX]], i8 [[MINXZ]], i8 [[MINYZ]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp ugt i8 %x, %z
+; CHECK-NEXT:    [[TMP2:%.*]] = select i1 [[TMP1]], i8 %x, i8 %z
+; CHECK-NEXT:    [[TMP3:%.*]] = icmp ugt i8 %y, %z
+; CHECK-NEXT:    [[TMP4:%.*]] = select i1 [[TMP3]], i8 %y, i8 %z
+; CHECK-NEXT:    [[R_V:%.*]] = select i1 [[CMPYX]], i8 [[TMP2]], i8 [[TMP4]]
+; CHECK-NEXT:    [[R:%.*]] = xor i8 [[R:%.*]].v, -1
 ; CHECK-NEXT:    ret i8 [[R]]
 ;
   %nx = xor i8 %x, -1