[llvm] 4baf29e - [DAG] Handle cases where a shift amount is larger than the pre-extended value bitwidth
Simon Pilgrim via llvm-commits
llvm-commits at lists.llvm.org
Tue Aug 27 10:15:25 PDT 2024
Author: Simon Pilgrim
Date: 2024-08-27T18:12:24+01:00
New Revision: 4baf29e81e30e6ebc1da56b9e5c338014961acf9
URL: https://github.com/llvm/llvm-project/commit/4baf29e81e30e6ebc1da56b9e5c338014961acf9
DIFF: https://github.com/llvm/llvm-project/commit/4baf29e81e30e6ebc1da56b9e5c338014961acf9.diff
LOG: [DAG] Handle cases where a shift amount is larger than the pre-extended value bitwidth
In the (zext (shl (zext x), cst)) -> (shl (zext x), cst) fold, don't use a bitmask / MaskedValueIsZero as we can't guarantee that the shift amount is in bounds.
Fixes #106202
Added:
llvm/test/CodeGen/SystemZ/pr106202.ll
Modified:
llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index b27f06f94ff0e7..b0a906743f29ff 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -14114,13 +14114,10 @@ SDValue DAGCombiner::visitZERO_EXTEND(SDNode *N) {
if (ShAmtC->getAPIntValue().ugt(KnownZeroBits)) {
// If the shift is too large, then see if we can deduce that the
// shift is safe anyway.
- // Create a mask that has ones for the bits being shifted out.
- APInt ShiftOutMask =
- APInt::getHighBitsSet(ShVal.getValueSizeInBits(),
- ShAmtC->getAPIntValue().getZExtValue());
// Check if the bits being shifted out are known to be zero.
- if (!DAG.MaskedValueIsZero(ShVal, ShiftOutMask))
+ KnownBits KnownShVal = DAG.computeKnownBits(ShVal);
+ if (ShAmtC->getAPIntValue().ugt(KnownShVal.countMinLeadingZeros()))
return SDValue();
}
}
diff --git a/llvm/test/CodeGen/SystemZ/pr106202.ll b/llvm/test/CodeGen/SystemZ/pr106202.ll
new file mode 100644
index 00000000000000..7ec165e932eace
--- /dev/null
+++ b/llvm/test/CodeGen/SystemZ/pr106202.ll
@@ -0,0 +1,31 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=s390x-ibm-linux -mcpu=z10 | FileCheck %s
+
+ at g_0 = external dso_local local_unnamed_addr global i16, align 2
+ at g_1 = external dso_local local_unnamed_addr global i32, align 4
+ at g_2 = external dso_local local_unnamed_addr global i32, align 4
+
+define void @func() {
+; CHECK-LABEL: func:
+; CHECK: # %bb.0:
+; CHECK-NEXT: lhi %r0, 41
+; CHECK-NEXT: strl %r0, g_1
+; CHECK-NEXT: lhi %r0, 0
+; CHECK-NEXT: strl %r0, g_2
+; CHECK-NEXT: br %r14
+ store i32 41, ptr @g_1, align 4
+ %1 = load i32, ptr @g_1, align 4
+ %2 = load i16, ptr @g_0, align 2
+ %3 = zext i16 %2 to i32
+ %4 = shl i32 %3, %1
+ %5 = zext i32 %4 to i64
+ %6 = shl i64 %5, 48
+ %7 = ashr exact i64 %6, 48
+ %8 = or i64 %7, 0
+ %9 = sext i32 %1 to i64
+ %10 = icmp sge i64 %8, %9
+ %11 = zext i1 %10 to i32
+ %12 = or i32 0, %11
+ store i32 %12, ptr @g_2, align 4
+ ret void
+}
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