[llvm] d50c1fc - [InstCombine] Fold `(icmp eq/ne (zext i1 X) (sext i1 Y))`-> `(icmp eq/ne (or X, Y), 0)`

[Noah Goldstein via llvm-commits]

Author: Noah Goldstein
Date: 2023-07-12T17:17:52-05:00
New Revision: d50c1fcb5d3ce0a5f2da5ef8f61ac730a213509b

URL: https://github.com/llvm/llvm-project/commit/d50c1fcb5d3ce0a5f2da5ef8f61ac730a213509b
DIFF: https://github.com/llvm/llvm-project/commit/d50c1fcb5d3ce0a5f2da5ef8f61ac730a213509b.diff

LOG: [InstCombine] Fold `(icmp eq/ne (zext i1 X) (sext i1 Y))`-> `(icmp eq/ne (or X, Y), 0)`

This comes up when adding two `bool` types in C/C++
```
    bool foo(bool a, bool b) {
        return a + b;
    }
    ...
    ->
    define i1 @foo(i1 %a, i1 %b) {
        %conv = zext i1 %a to i32
        %conv3.neg = sext i1 %b to i32
        %tobool4 = icmp ne i32 %conv, %conv3.neg
        ret i1 %tobool4
}
```

Proof: https://alive2.llvm.org/ce/z/HffWAN

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D154574

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/icmp-ext-ext.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 4c1272b0a8b3b3..4a282bee362e3b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -5260,10 +5260,19 @@ Instruction *InstCombinerImpl::foldICmpWithZextOrSext(ICmpInst &ICmp) {
     bool IsZext0 = isa<ZExtOperator>(ICmp.getOperand(0));
     bool IsZext1 = isa<ZExtOperator>(ICmp.getOperand(1));
 
-    // If we have mismatched casts, treat the zext of a non-negative source as
-    // a sext to simulate matching casts. Otherwise, we are done.
-    // TODO: Can we handle some predicates (equality) without non-negative?
     if (IsZext0 != IsZext1) {
+        // If X and Y and both i1
+        // (icmp eq/ne (zext X) (sext Y))
+        //      eq -> (icmp eq (or X, Y), 0)
+        //      ne -> (icmp ne (or X, Y), 0)
+      if (ICmp.isEquality() && X->getType()->isIntOrIntVectorTy(1) &&
+          Y->getType()->isIntOrIntVectorTy(1))
+        return new ICmpInst(ICmp.getPredicate(), Builder.CreateOr(X, Y),
+                            Constant::getNullValue(X->getType()));
+
+      // If we have mismatched casts, treat the zext of a non-negative source as
+      // a sext to simulate matching casts. Otherwise, we are done.
+      // TODO: Can we handle some predicates (equality) without non-negative?
       if ((IsZext0 && isKnownNonNegative(X, DL, 0, &AC, &ICmp, &DT)) ||
           (IsZext1 && isKnownNonNegative(Y, DL, 0, &AC, &ICmp, &DT)))
         IsSignedExt = true;

diff  --git a/llvm/test/Transforms/InstCombine/icmp-ext-ext.ll b/llvm/test/Transforms/InstCombine/icmp-ext-ext.ll
index c350358f488edb..b3dafe06a38799 100644
--- a/llvm/test/Transforms/InstCombine/icmp-ext-ext.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-ext-ext.ll
@@ -384,9 +384,8 @@ define i1 @sext_zext_uge_known_nonneg_op0_wide(i16 %x, i8 %y) {
 
 define i1 @zext_eq_sext(i1 %a, i1 %b) {
 ; CHECK-LABEL: @zext_eq_sext(
-; CHECK-NEXT:    [[CONV:%.*]] = zext i1 [[A:%.*]] to i32
-; CHECK-NEXT:    [[CONV3_NEG:%.*]] = sext i1 [[B:%.*]] to i32
-; CHECK-NEXT:    [[TOBOOL4:%.*]] = icmp eq i32 [[CONV]], [[CONV3_NEG]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or i1 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[TOBOOL4:%.*]] = xor i1 [[TMP1]], true
 ; CHECK-NEXT:    ret i1 [[TOBOOL4]]
 ;
   %conv = zext i1 %a to i32
@@ -410,10 +409,8 @@ define i1 @zext_eq_sext_fail_not_i1(i1 %a, i8 %b) {
 
 define <2 x i1> @zext_ne_sext(<2 x i1> %a, <2 x i1> %b) {
 ; CHECK-LABEL: @zext_ne_sext(
-; CHECK-NEXT:    [[CONV:%.*]] = zext <2 x i1> [[A:%.*]] to <2 x i8>
-; CHECK-NEXT:    [[CONV3_NEG:%.*]] = sext <2 x i1> [[B:%.*]] to <2 x i8>
-; CHECK-NEXT:    [[TOBOOL4:%.*]] = icmp ne <2 x i8> [[CONV3_NEG]], [[CONV]]
-; CHECK-NEXT:    ret <2 x i1> [[TOBOOL4]]
+; CHECK-NEXT:    [[TMP1:%.*]] = or <2 x i1> [[B:%.*]], [[A:%.*]]
+; CHECK-NEXT:    ret <2 x i1> [[TMP1]]
 ;
   %conv = zext <2 x i1> %a to <2 x i8>
   %conv3.neg = sext <2 x i1> %b to <2 x i8>