From: Sanjay Patel <spatel@rotateright.com>
Date: Wed, 6 Dec 2017 21:22:57 +0000 (+0000)
Subject: [InstCombine] canonicalize constant-minus-boolean to select-of-constants
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2b68e112a31ad72dc10bee5fb430fe3ea8d63489;p=llvm

[InstCombine] canonicalize constant-minus-boolean to select-of-constants

This restores the half of:
https://reviews.llvm.org/rL75531
that was reverted at:
https://reviews.llvm.org/rL159230

For the x86 case mentioned there, we now produce:
leal 1(%rdi), %eax
subl %esi, %eax

We have target hooks to invert this in DAGCombiner (and x86 is enabled) with:
https://reviews.llvm.org/rL296977
https://reviews.llvm.org/rL311731

AArch64 and possibly other targets would probably benefit from enabling those hooks too.
See PR30327:
https://bugs.llvm.org/show_bug.cgi?id=30327#c2

Differential Revision: https://reviews.llvm.org/D40612


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@319964 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index d28d615f47e..68889764484 100644
--- a/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1520,8 +1520,13 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
     return BinaryOperator::CreateNot(Op1);
 
   if (Constant *C = dyn_cast<Constant>(Op0)) {
+    Value *X;
+    // C - zext(bool) -> bool ? C - 1 : C
+    if (match(Op1, m_ZExt(m_Value(X))) &&
+        X->getType()->getScalarSizeInBits() == 1)
+      return SelectInst::Create(X, SubOne(C), C);
+
     // C - ~X == X + (1+C)
-    Value *X = nullptr;
     if (match(Op1, m_Not(m_Value(X))))
       return BinaryOperator::CreateAdd(X, AddOne(C));
 
diff --git a/test/Transforms/InstCombine/zext-bool-add-sub.ll b/test/Transforms/InstCombine/zext-bool-add-sub.ll
index 5a5b092c4d8..81f27aa095c 100644
--- a/test/Transforms/InstCombine/zext-bool-add-sub.ll
+++ b/test/Transforms/InstCombine/zext-bool-add-sub.ll
@@ -20,8 +20,7 @@ define i32 @a(i1 zeroext %x, i1 zeroext %y) {
 
 define i32 @zextsub(i1 %x) {
 ; CHECK-LABEL: @zextsub(
-; CHECK-NEXT:    [[ZEXT:%.*]] = zext i1 %x to i32
-; CHECK-NEXT:    [[SUB:%.*]] = sub nsw i32 11, [[ZEXT]]
+; CHECK-NEXT:    [[SUB:%.*]] = select i1 %x, i32 10, i32 11
 ; CHECK-NEXT:    ret i32 [[SUB]]
 ;
   %zext = zext i1 %x to i32
@@ -31,8 +30,7 @@ define i32 @zextsub(i1 %x) {
 
 define <2 x i32> @zextsub_splat(<2 x i1> %x) {
 ; CHECK-LABEL: @zextsub_splat(
-; CHECK-NEXT:    [[ZEXT:%.*]] = zext <2 x i1> %x to <2 x i32>
-; CHECK-NEXT:    [[SUB:%.*]] = sub nsw <2 x i32> <i32 42, i32 42>, [[ZEXT]]
+; CHECK-NEXT:    [[SUB:%.*]] = select <2 x i1> %x, <2 x i32> <i32 41, i32 41>, <2 x i32> <i32 42, i32 42>
 ; CHECK-NEXT:    ret <2 x i32> [[SUB]]
 ;
   %zext = zext <2 x i1> %x to <2 x i32>
@@ -42,8 +40,7 @@ define <2 x i32> @zextsub_splat(<2 x i1> %x) {
 
 define <2 x i32> @zextsub_vec(<2 x i1> %x) {
 ; CHECK-LABEL: @zextsub_vec(
-; CHECK-NEXT:    [[ZEXT:%.*]] = zext <2 x i1> %x to <2 x i32>
-; CHECK-NEXT:    [[SUB:%.*]] = sub nsw <2 x i32> <i32 11, i32 42>, [[ZEXT]]
+; CHECK-NEXT:    [[SUB:%.*]] = select <2 x i1> %x, <2 x i32> <i32 10, i32 41>, <2 x i32> <i32 11, i32 42>
 ; CHECK-NEXT:    ret <2 x i32> [[SUB]]
 ;
   %zext = zext <2 x i1> %x to <2 x i32>