From 79b1ca8ebdeb2bc8c20fceb53b95959526a0b716 Mon Sep 17 00:00:00 2001
From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Tue, 2 Aug 2022 11:38:47 +0100
Subject: [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.

(cherry picked from commit b651fdff79027064071db7c1d0250553e3e6a232)
---
 llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp | 26 ++++++++++--------
 llvm/test/CodeGen/X86/rotate5.ll              | 39 +++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 11 deletions(-)
 create mode 100644 llvm/test/CodeGen/X86/rotate5.ll

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 654879115ff9..a367ea51be30 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -7301,12 +7301,14 @@ 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;
+      }
     }
   }
 
@@ -7322,11 +7324,13 @@ 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 000000000000..b1f38f87ec89
--- /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
+}
-- 
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