[llvm] c727b48 - [SDAG][ISel][TableGen][LoongArch] Report error for trivial bitcasts when there are predicate calls (#116075)

[via llvm-commits]

Author: Yingwei Zheng
Date: 2024-11-19T21:24:40+08:00
New Revision: c727b48287cc96888f9e262f23d53cf635cf3b3d

URL: https://github.com/llvm/llvm-project/commit/c727b48287cc96888f9e262f23d53cf635cf3b3d
DIFF: https://github.com/llvm/llvm-project/commit/c727b48287cc96888f9e262f23d53cf635cf3b3d.diff

LOG: [SDAG][ISel][TableGen][LoongArch] Report error for trivial bitcasts when there are predicate calls (#116075)

On loongarch64 with lsx extension, we select `VBITREV_W` for `v4i32 (xor
X, (shl splat(1), Y))`:

https://github.com/llvm/llvm-project/blob/8e6630391699116641cf390a10476295b7d4b95c/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td#L1583-L1584

And `vsplat_imm_eq_1` is defined as:

https://github.com/llvm/llvm-project/blob/8e6630391699116641cf390a10476295b7d4b95c/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td#L77-L87

For the `(bitconvert (v4i32 (build_vector)))` case, the pattern is
expected to be:
```
PATTERN: (xor:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, (shl:{ *:[v4i32] } (bitconvert:{ *:[v4i32] } (build_vector:{ *:[v4i32] }))<<P:Predicate_vsplat_imm_eq_1>>, v4i32:{ *:[v4i32] }:$vk))
RESULT:  (VBITREV_W:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, v4i32:{ *:[v4i32] }:$vk)
```

However, `simplifyTree` drops the `bitconvert` node and its predicates:

https://github.com/llvm/llvm-project/blob/8e6630391699116641cf390a10476295b7d4b95c/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp#L3036-L3062

Then llvm will match `vsplat_imm_eq_1` for any v4i32 splats and cause a
miscompilation:
```
PATTERN: (xor:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, (shl:{ *:[v4i32] } (build_vector:{ *:[v4i32] }), v4i32:{ *:[v4i32] }:$vk))
RESULT:  (VBITREV_W:{ *:[v4i32] } v4i32:{ *:[v4i32] }:$vj, v4i32:{ *:[v4i32] }:$vk)
```

This patch adds additional checks for predicates associated with the
trivial bitconvert node. Unused patterns in the LoongArch target are
also removed.

Fixes https://github.com/llvm/llvm-project/issues/116008.

Added: 
    llvm/test/CodeGen/LoongArch/lsx/pr116008.ll

Modified: 
    llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td
    llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td b/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td
index 250896cbbe5f7a..1a267b3e42a30d 100644
--- a/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td
+++ b/llvm/lib/Target/LoongArch/LoongArchLSXInstrInfo.td
@@ -74,8 +74,7 @@ class VecCond<SDPatternOperator OpNode, ValueType TyNode,
   let usesCustomInserter = 1;
 }
 
-def vsplat_imm_eq_1 : PatFrags<(ops), [(build_vector),
-                                       (bitconvert (v4i32 (build_vector)))], [{
+def vsplat_imm_eq_1 : PatFrags<(ops), [(build_vector)], [{
   APInt Imm;
   EVT EltTy = N->getValueType(0).getVectorElementType();
 
@@ -116,8 +115,7 @@ def vsplati32_imm_eq_31 : PatFrags<(ops), [(build_vector)], [{
   return selectVSplat(N, Imm, EltTy.getSizeInBits()) &&
          Imm.getBitWidth() == EltTy.getSizeInBits() && Imm == 31;
 }]>;
-def vsplati64_imm_eq_63 : PatFrags<(ops), [(build_vector),
-                                           (bitconvert (v4i32 (build_vector)))], [{
+def vsplati64_imm_eq_63 : PatFrags<(ops), [(build_vector)], [{
   APInt Imm;
   EVT EltTy = N->getValueType(0).getVectorElementType();
 

diff  --git a/llvm/test/CodeGen/LoongArch/lsx/pr116008.ll b/llvm/test/CodeGen/LoongArch/lsx/pr116008.ll
new file mode 100644
index 00000000000000..ba8ffc34931893
--- /dev/null
+++ b/llvm/test/CodeGen/LoongArch/lsx/pr116008.ll
@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc --mtriple=loongarch64 --mattr=+lsx < %s | FileCheck %s
+
+define <4 x i32> @xor_shl_splat_vec_one(i32 %x, <4 x i32> %y) nounwind {
+; CHECK-LABEL: xor_shl_splat_vec_one:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    vreplgr2vr.w $vr1, $a0
+; CHECK-NEXT:    vsll.w $vr0, $vr1, $vr0
+; CHECK-NEXT:    vbitrevi.w $vr0, $vr0, 0
+; CHECK-NEXT:    ret
+entry:
+  %ins = insertelement <4 x i32> poison, i32 %x, i64 0
+  %splat = shufflevector <4 x i32> %ins, <4 x i32> poison, <4 x i32> zeroinitializer
+  %shl = shl <4 x i32> %splat, %y
+  %xor = xor <4 x i32> %shl, splat (i32 1)
+  ret <4 x i32> %xor
+}

diff  --git a/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp b/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
index c8186d6e69523f..163a1a78a2ec40 100644
--- a/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
+++ b/llvm/utils/TableGen/Common/CodeGenDAGPatterns.cpp
@@ -3056,6 +3056,14 @@ static bool SimplifyTree(TreePatternNodePtr &N) {
       !N->getExtType(0).empty() &&
       N->getExtType(0) == N->getChild(0).getExtType(0) &&
       N->getName().empty()) {
+    if (!N->getPredicateCalls().empty()) {
+      std::string Str;
+      raw_string_ostream OS(Str);
+      OS << *N
+         << "\n trivial bitconvert node should not have predicate calls\n";
+      PrintFatalError(Str);
+      return false;
+    }
     N = N->getChildShared(0);
     SimplifyTree(N);
     return true;