[llvm] 63d4e0f - [InstCombine] Compute result directly on APInts

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2025-01-07T12:13:19+01:00
New Revision: 63d4e0fb66b75dd1c60acaa81ff8f8a4327cffcc

URL: https://github.com/llvm/llvm-project/commit/63d4e0fb66b75dd1c60acaa81ff8f8a4327cffcc
DIFF: https://github.com/llvm/llvm-project/commit/63d4e0fb66b75dd1c60acaa81ff8f8a4327cffcc.diff

LOG: [InstCombine] Compute result directly on APInts

If the bitwidth is 2 and we add two 1s, the result may overflow.
This is fine in terms of correctness, but triggers the APInt ctor
assertion. Fix this by performing the calculation directly on APInts.

Fixes the issue reported in:
https://github.com/llvm/llvm-project/pull/114539#issuecomment-2574845003

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 8b23583c510637..d764f845ffd430 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3091,12 +3091,12 @@ Instruction *InstCombinerImpl::foldICmpAddConstant(ICmpInst &Cmp,
     unsigned BW = C.getBitWidth();
     std::bitset<4> Table;
     auto ComputeTable = [&](bool Op0Val, bool Op1Val) {
-      int Res = 0;
+      APInt Res(BW, 0);
       if (Op0Val)
-        Res += isa<ZExtInst>(Ext0) ? 1 : -1;
+        Res += APInt(BW, isa<ZExtInst>(Ext0) ? 1 : -1, /*isSigned=*/true);
       if (Op1Val)
-        Res += isa<ZExtInst>(Ext1) ? 1 : -1;
-      return ICmpInst::compare(APInt(BW, Res, true), C, Pred);
+        Res += APInt(BW, isa<ZExtInst>(Ext1) ? 1 : -1, /*isSigned=*/true);
+      return ICmpInst::compare(Res, C, Pred);
     };
 
     Table[0] = ComputeTable(false, false);

diff  --git a/llvm/test/Transforms/InstCombine/icmp-add.ll b/llvm/test/Transforms/InstCombine/icmp-add.ll
index 579247aaccf282..a8cdf80948a840 100644
--- a/llvm/test/Transforms/InstCombine/icmp-add.ll
+++ b/llvm/test/Transforms/InstCombine/icmp-add.ll
@@ -79,6 +79,19 @@ bb:
   ret i1 %i4
 }
 
+define i1 @cvt_icmp_0_zext_plus_zext_eq_i2(i1 %a, i1 %b) {
+; CHECK-LABEL: @cvt_icmp_0_zext_plus_zext_eq_i2(
+; CHECK-NEXT:    [[TMP1:%.*]] = or i1 [[A:%.*]], [[B:%.*]]
+; CHECK-NEXT:    [[CMP:%.*]] = xor i1 [[TMP1]], true
+; CHECK-NEXT:    ret i1 [[CMP]]
+;
+  %a.ext = zext i1 %a to i2
+  %b.ext = zext i1 %b to i2
+  %add = add i2 %a.ext, %b.ext
+  %cmp = icmp eq i2 %add, 0
+  ret i1 %cmp
+}
+
 define i1 @cvt_icmp_1_zext_plus_zext_eq(i1 %arg, i1 %arg1) {
 ; CHECK-LABEL: @cvt_icmp_1_zext_plus_zext_eq(
 ; CHECK-NEXT:  bb: