[llvm] [RISCV][ISel] Allow opaque constants in `hasAndNotCompare` (PR #92926)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-risc-v

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

See the following code:

https://github.com/llvm/llvm-project/blob/4ae896fe979b7db501cabde4b6b3504478958682/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp#L9334-L9357

> Combining: t47: i64 = xor t43, OpaqueConstant:i64<31808>
X: i64 = Constant<0>
Y: i64 = OpaqueConstant<31808>

The assertion failed because both `X` and `Y` are constants.
This patch allows opaque constants in `hasAndNotCompare` to fix the issue. I think it is correct, as we have done this in other places:
https://github.com/llvm/llvm-project/blob/4ae896fe979b7db501cabde4b6b3504478958682/llvm/lib/Target/RISCV/RISCVISelLowering.cpp#L7496-L7504

Another solution is to comment out the assertion. But it produces worse codegen.

Fixes https://github.com/llvm/llvm-project/issues/90730.


---
Full diff: https://github.com/llvm/llvm-project/pull/92926.diff


2 Files Affected:

- (modified) llvm/lib/Target/RISCV/RISCVISelLowering.cpp (+1-1) 
- (added) llvm/test/CodeGen/RISCV/pr90730.ll (+22) 


``````````diff
diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 4961d2b6ba768..929ff7d2de2d0 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -1919,7 +1919,7 @@ bool RISCVTargetLowering::hasAndNotCompare(SDValue Y) const {
     return false;
 
   return (Subtarget.hasStdExtZbb() || Subtarget.hasStdExtZbkb()) &&
-         !isa<ConstantSDNode>(Y);
+         (!isa<ConstantSDNode>(Y) || cast<ConstantSDNode>(Y)->isOpaque());
 }
 
 bool RISCVTargetLowering::hasBitTest(SDValue X, SDValue Y) const {
diff --git a/llvm/test/CodeGen/RISCV/pr90730.ll b/llvm/test/CodeGen/RISCV/pr90730.ll
new file mode 100644
index 0000000000000..7c3f4b43089cb
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/pr90730.ll
@@ -0,0 +1,22 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc < %s -mtriple=riscv64 -mattr=+zbb | FileCheck %s
+
+define i32 @pr90730(i32 %x, i1 %y, ptr %p) {
+; CHECK-LABEL: pr90730:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    lui a1, 8
+; CHECK-NEXT:    addiw a1, a1, -960
+; CHECK-NEXT:    andn a0, a1, a0
+; CHECK-NEXT:    sw zero, 0(a2)
+; CHECK-NEXT:    ret
+entry:
+  %ext = zext i1 %y to i32
+  %xor1 = xor i32 %ext, 31817
+  %and1 = and i32 %xor1, %x
+  store i32 %and1, ptr %p, align 4
+  %v = load i32, ptr %p, align 4
+  %and2 = and i32 %v, 31808
+  %xor2 = xor i32 %and2, 31808
+  store i32 0, ptr %p, align 4
+  ret i32 %xor2
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/92926