[PATCH] D153148: [InstCombine] Fold `(-1 + zext(B)) & X` into `B ? 0 : X` where B is effectively a bool

[Yingwei Zheng via Phabricator via llvm-commits]

dtcxzyw created this revision.
dtcxzyw added reviewers: nikic, RKSimon, goldstein.w.n.
Herald added subscribers: StephenFan, hiraditya.
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Solves issue https://github.com/llvm/llvm-project/issues/63321.

This patch explicitly folds `(-1 + zext(B)) & X` into `B ? 0 : X`. Additional trunc will be created when `B` is neither i1 nor <N x i1>.

https://alive2.llvm.org/ce/z/pWv9jJ


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D153148

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  llvm/test/Transforms/InstCombine/binop-cast.ll


Index: llvm/test/Transforms/InstCombine/binop-cast.ll
===================================================================
--- llvm/test/Transforms/InstCombine/binop-cast.ll
+++ llvm/test/Transforms/InstCombine/binop-cast.ll
@@ -257,3 +257,17 @@
   %r = xor i32 %sext, 42
   ret i32 %r
 }
+
+define i64 @PR63321(ptr %ptr, i64 %c) {
+; CHECK-LABEL: @PR63321(
+; CHECK-NEXT:    [[VAL:%.*]] = load i8, ptr [[PTR:%.*]], align 1, !range [[RNG0:![0-9]+]]
+; CHECK-NEXT:    [[DOTNOT:%.*]] = icmp eq i8 [[VAL]], 0
+; CHECK-NEXT:    [[RES:%.*]] = select i1 [[DOTNOT]], i64 [[C:%.*]], i64 0
+; CHECK-NEXT:    ret i64 [[RES]]
+;
+  %val = load i8, ptr %ptr, align 1, !range !{i8 0, i8 2}
+  %rhs = zext i8 %val to i64
+  %mask = add i64 -1, %rhs
+  %res = and i64 %mask, %c
+  ret i64 %res
+}
Index: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2564,6 +2564,21 @@
       A->getType()->isIntOrIntVectorTy(1))
     return SelectInst::Create(A, Constant::getNullValue(Ty), Op0);
 
+  // (-1 + zext(A)) & Op1 --> A ? 0 : Op1
+  // Op0 & (-1 + zext(A)) --> A ? 0 : Op0
+  if (match(Op0, m_NSWAdd(m_ZExt(m_Value(A)), m_AllOnes())) &&
+      (A->getType()->isIntOrIntVectorTy(1) ||
+       (~computeKnownBits(A, 0, dyn_cast<Instruction>(Op0)).Zero) == 1))
+    return SelectInst::Create(
+        Builder.CreateTrunc(A, A->getType()->getWithNewBitWidth(1)),
+        Constant::getNullValue(Ty), Op1);
+  if (match(Op1, m_NSWAdd(m_ZExt(m_Value(A)), m_AllOnes())) &&
+      (A->getType()->isIntOrIntVectorTy(1) ||
+       (~computeKnownBits(A, 0, dyn_cast<Instruction>(Op1)).Zero) == 1))
+    return SelectInst::Create(
+        Builder.CreateTrunc(A, A->getType()->getWithNewBitWidth(1)),
+        Constant::getNullValue(Ty), Op0);
+
   // (iN X s>> (N-1)) & Y --> (X s< 0) ? Y : 0 -- with optional sext
   if (match(&I, m_c_And(m_OneUse(m_SExtOrSelf(
                             m_AShr(m_Value(X), m_APIntAllowUndef(C)))),


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