[llvm] b651fdf - [DAG] matchRotateSub - ensure the (pre-extended) shift amount is wide enough for the amount mask (PR56859)

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2022-08-02T11:38:52+01:00
New Revision: b651fdff79027064071db7c1d0250553e3e6a232

URL: https://github.com/llvm/llvm-project/commit/b651fdff79027064071db7c1d0250553e3e6a232
DIFF: https://github.com/llvm/llvm-project/commit/b651fdff79027064071db7c1d0250553e3e6a232.diff

LOG: [DAG] matchRotateSub - ensure the (pre-extended) shift amount is wide enough for the amount mask (PR56859)

matchRotateSub is given shift amounts that will already have stripped any/zero-extend nodes from - so make sure those values are wide enough to take a mask.

Added: 
    llvm/test/CodeGen/X86/rotate5.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 2d6e0e836710d..18cee00bcd3f7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7317,12 +7317,14 @@ static bool matchRotateSub(SDValue Pos, SDValue Neg, unsigned EltSize,
   unsigned MaskLoBits = 0;
   if (IsRotate && isPowerOf2_64(EltSize)) {
     unsigned Bits = Log2_64(EltSize);
-    APInt DemandedBits =
-        APInt::getLowBitsSet(Neg.getScalarValueSizeInBits(), Bits);
-    if (SDValue Inner =
-            TLI.SimplifyMultipleUseDemandedBits(Neg, DemandedBits, DAG)) {
-      Neg = Inner;
-      MaskLoBits = Bits;
+    unsigned NegBits = Neg.getScalarValueSizeInBits();
+    if (NegBits >= Bits) {
+      APInt DemandedBits = APInt::getLowBitsSet(NegBits, Bits);
+      if (SDValue Inner =
+              TLI.SimplifyMultipleUseDemandedBits(Neg, DemandedBits, DAG)) {
+        Neg = Inner;
+        MaskLoBits = Bits;
+      }
     }
   }
 
@@ -7338,11 +7340,13 @@ static bool matchRotateSub(SDValue Pos, SDValue Neg, unsigned EltSize,
   // affect Mask's demanded bits, just replace Pos with Pos'. These operations
   // are redundant for the purpose of the equality.
   if (MaskLoBits) {
-    APInt DemandedBits =
-        APInt::getLowBitsSet(Pos.getScalarValueSizeInBits(), MaskLoBits);
-    if (SDValue Inner =
-            TLI.SimplifyMultipleUseDemandedBits(Pos, DemandedBits, DAG)) {
-      Pos = Inner;
+    unsigned PosBits = Pos.getScalarValueSizeInBits();
+    if (PosBits >= MaskLoBits) {
+      APInt DemandedBits = APInt::getLowBitsSet(PosBits, MaskLoBits);
+      if (SDValue Inner =
+              TLI.SimplifyMultipleUseDemandedBits(Pos, DemandedBits, DAG)) {
+        Pos = Inner;
+      }
     }
   }
 

diff  --git a/llvm/test/CodeGen/X86/rotate5.ll b/llvm/test/CodeGen/X86/rotate5.ll
new file mode 100644
index 0000000000000..b1f38f87ec895
--- /dev/null
+++ b/llvm/test/CodeGen/X86/rotate5.ll
@@ -0,0 +1,39 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=i686-unknown-unknown | FileCheck %s --check-prefixes=X86
+; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s --check-prefixes=X64
+
+; Ensure that the (pre-extended) shift amount type is wide enough to take any mask.
+define void @PR56859() {
+; X86-LABEL: PR56859:
+; X86:       # %bb.0: # %entry
+; X86-NEXT:    movl (%eax), %ecx
+; X86-NEXT:    testl %ecx, %ecx
+; X86-NEXT:    setne %al
+; X86-NEXT:    movl $1, %edx
+; X86-NEXT:    # kill: def $cl killed $cl killed $ecx
+; X86-NEXT:    shrl %cl, %edx
+; X86-NEXT:    btsl %eax, %edx
+; X86-NEXT:    movl %edx, (%eax)
+; X86-NEXT:    retl
+;
+; X64-LABEL: PR56859:
+; X64:       # %bb.0: # %entry
+; X64-NEXT:    movl (%rax), %ecx
+; X64-NEXT:    testl %ecx, %ecx
+; X64-NEXT:    setne %al
+; X64-NEXT:    movl $1, %edx
+; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
+; X64-NEXT:    shrl %cl, %edx
+; X64-NEXT:    btsl %eax, %edx
+; X64-NEXT:    movl %edx, (%rax)
+; X64-NEXT:    retq
+entry:
+  %0 = load i32, ptr undef, align 4
+  %tobool = icmp ne i32 %0, 0
+  %lor.ext = zext i1 %tobool to i32
+  %shr = lshr i32 1, %0
+  %shl = shl i32 1, %lor.ext
+  %or = or i32 %shl, %shr
+  store i32 %or, ptr undef, align 4
+  ret void
+}