[llvm] [GlobalIsel] Combine freeze (PR #93239)

[Dhruv Chawla via llvm-commits]

Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>,
Thorsten =?utf-8?q?Schütt?= <schuett at gmail.com>
Message-ID:
In-Reply-To: <llvm.org/llvm/llvm-project/pull/93239 at github.com>


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@@ -1724,6 +1724,39 @@ bool llvm::isPreISelGenericFloatingPointOpcode(unsigned Opc) {
   }
 }
 
+/// Shifts return poison if shiftwidth is larger than the bitwidth.
+static bool shiftAmountKnownInRange(Register ShiftAmount,
+                                    const MachineRegisterInfo &MRI) {
+  LLT Ty = MRI.getType(ShiftAmount);
+
+  if (Ty.isScalableVector())
+    return false; // Can't tell, just return false to be safe
+
+  if (Ty.isScalar()) {
+    std::optional<ValueAndVReg> Val =
+        getIConstantVRegValWithLookThrough(ShiftAmount, MRI);
+    if (!Val)
+      return false;
+    return Val->Value.ult(Ty.getScalarSizeInBits());
+  }
+
+  GBuildVector *BV = getOpcodeDef<GBuildVector>(ShiftAmount, MRI);
+  if (!BV)
+    return false;
+
+  unsigned Sources = BV->getNumSources();
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dc03-work wrote:

Should add a comment explaining why `GBuildVector` specifically is being checked.

https://github.com/llvm/llvm-project/pull/93239