[llvm] [llvm-exegesis] Use older instructions to load lower vregs (PR #114768)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-tools-llvm-exegesis

Author: Aiden Grossman (boomanaiden154)

<details>
<summary>Changes</summary>

This patch makes X86 llvm-exegesis unconditionally use older instructions to load the lower vector registers, rather than trying to use AVX512 for everything when available. This fixes a case where we would try and load AVX512 registers using the older instructions if such a snippet was constructed while -mcpu was set to something that did not support AVX512. This would lead to a machine code verification error rather than resulting in incomplete snippet setup, which seems to be the intention of how this should work.

Fixes #<!-- -->114691.

---
Full diff: https://github.com/llvm/llvm-project/pull/114768.diff


2 Files Affected:

- (modified) llvm/tools/llvm-exegesis/lib/X86/Target.cpp (+8-4) 
- (modified) llvm/unittests/tools/llvm-exegesis/X86/TargetTest.cpp (+36-4) 


``````````diff
diff --git a/llvm/tools/llvm-exegesis/lib/X86/Target.cpp b/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
index 4709dede5b2e20..0a70321fab7818 100644
--- a/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
+++ b/llvm/tools/llvm-exegesis/lib/X86/Target.cpp
@@ -1054,18 +1054,22 @@ std::vector<MCInst> ExegesisX86Target::setRegTo(const MCSubtargetInfo &STI,
   ConstantInliner CI(Value);
   if (X86::VR64RegClass.contains(Reg))
     return CI.loadAndFinalize(Reg, 64, X86::MMX_MOVQ64rm);
+  if (X86::VR128RegClass.contains(Reg)) {
+    if (STI.getFeatureBits()[X86::FeatureAVX])
+      return CI.loadAndFinalize(Reg, 128, X86::VMOVDQUrm);
+    return CI.loadAndFinalize(Reg, 128, X86::MOVDQUrm);
+  }
   if (X86::VR128XRegClass.contains(Reg)) {
     if (STI.getFeatureBits()[X86::FeatureAVX512])
       return CI.loadAndFinalize(Reg, 128, X86::VMOVDQU32Z128rm);
+  }
+  if (X86::VR256RegClass.contains(Reg)) {
     if (STI.getFeatureBits()[X86::FeatureAVX])
-      return CI.loadAndFinalize(Reg, 128, X86::VMOVDQUrm);
-    return CI.loadAndFinalize(Reg, 128, X86::MOVDQUrm);
+      return CI.loadAndFinalize(Reg, 256, X86::VMOVDQUYrm);
   }
   if (X86::VR256XRegClass.contains(Reg)) {
     if (STI.getFeatureBits()[X86::FeatureAVX512])
       return CI.loadAndFinalize(Reg, 256, X86::VMOVDQU32Z256rm);
-    if (STI.getFeatureBits()[X86::FeatureAVX])
-      return CI.loadAndFinalize(Reg, 256, X86::VMOVDQUYrm);
   }
   if (X86::VR512RegClass.contains(Reg))
     if (STI.getFeatureBits()[X86::FeatureAVX512])
diff --git a/llvm/unittests/tools/llvm-exegesis/X86/TargetTest.cpp b/llvm/unittests/tools/llvm-exegesis/X86/TargetTest.cpp
index 3a028bad486ccc..921d7d7975f6ae 100644
--- a/llvm/unittests/tools/llvm-exegesis/X86/TargetTest.cpp
+++ b/llvm/unittests/tools/llvm-exegesis/X86/TargetTest.cpp
@@ -242,7 +242,20 @@ TEST_F(X86Core2AvxTargetTest, SetRegToVR128Value_Use_VMOVDQUrm) {
                   IsStackDeallocate(16)));
 }
 
-TEST_F(X86Core2Avx512TargetTest, SetRegToVR128Value_Use_VMOVDQU32Z128rm) {
+TEST_F(X86Core2Avx512TargetTest,
+       SetRegToVR128ValueHighXMM_Use_VMOVDQU32Z128rm) {
+  EXPECT_THAT(
+      setRegTo(X86::XMM16, APInt(128, "11112222333344445555666677778888", 16)),
+      ElementsAre(IsStackAllocate(16),
+                  IsMovValueToStack(X86::MOV32mi, 0x77778888UL, 0),
+                  IsMovValueToStack(X86::MOV32mi, 0x55556666UL, 4),
+                  IsMovValueToStack(X86::MOV32mi, 0x33334444UL, 8),
+                  IsMovValueToStack(X86::MOV32mi, 0x11112222UL, 12),
+                  IsMovValueFromStack(X86::VMOVDQU32Z128rm, X86::XMM16),
+                  IsStackDeallocate(16)));
+}
+
+TEST_F(X86Core2Avx512TargetTest, SetRegToVR128ValueLowXMM_Use_VMOVDQUrm) {
   EXPECT_THAT(
       setRegTo(X86::XMM0, APInt(128, "11112222333344445555666677778888", 16)),
       ElementsAre(IsStackAllocate(16),
@@ -250,7 +263,7 @@ TEST_F(X86Core2Avx512TargetTest, SetRegToVR128Value_Use_VMOVDQU32Z128rm) {
                   IsMovValueToStack(X86::MOV32mi, 0x55556666UL, 4),
                   IsMovValueToStack(X86::MOV32mi, 0x33334444UL, 8),
                   IsMovValueToStack(X86::MOV32mi, 0x11112222UL, 12),
-                  IsMovValueFromStack(X86::VMOVDQU32Z128rm, X86::XMM0),
+                  IsMovValueFromStack(X86::VMOVDQUrm, X86::XMM0),
                   IsStackDeallocate(16)));
 }
 
@@ -272,7 +285,26 @@ TEST_F(X86Core2AvxTargetTest, SetRegToVR256Value_Use_VMOVDQUYrm) {
                         IsStackDeallocate(32)}));
 }
 
-TEST_F(X86Core2Avx512TargetTest, SetRegToVR256Value_Use_VMOVDQU32Z256rm) {
+TEST_F(X86Core2Avx512TargetTest,
+       SetRegToVR256ValueHighYMM_Use_VMOVDQU32Z256rm) {
+  const char ValueStr[] =
+      "1111111122222222333333334444444455555555666666667777777788888888";
+  EXPECT_THAT(
+      setRegTo(X86::YMM16, APInt(256, ValueStr, 16)),
+      ElementsAreArray({IsStackAllocate(32),
+                        IsMovValueToStack(X86::MOV32mi, 0x88888888UL, 0),
+                        IsMovValueToStack(X86::MOV32mi, 0x77777777UL, 4),
+                        IsMovValueToStack(X86::MOV32mi, 0x66666666UL, 8),
+                        IsMovValueToStack(X86::MOV32mi, 0x55555555UL, 12),
+                        IsMovValueToStack(X86::MOV32mi, 0x44444444UL, 16),
+                        IsMovValueToStack(X86::MOV32mi, 0x33333333UL, 20),
+                        IsMovValueToStack(X86::MOV32mi, 0x22222222UL, 24),
+                        IsMovValueToStack(X86::MOV32mi, 0x11111111UL, 28),
+                        IsMovValueFromStack(X86::VMOVDQU32Z256rm, X86::YMM16),
+                        IsStackDeallocate(32)}));
+}
+
+TEST_F(X86Core2Avx512TargetTest, SetRegToVR256ValueLowYMM_Use_VMOVDQUYrm) {
   const char ValueStr[] =
       "1111111122222222333333334444444455555555666666667777777788888888";
   EXPECT_THAT(
@@ -286,7 +318,7 @@ TEST_F(X86Core2Avx512TargetTest, SetRegToVR256Value_Use_VMOVDQU32Z256rm) {
                         IsMovValueToStack(X86::MOV32mi, 0x33333333UL, 20),
                         IsMovValueToStack(X86::MOV32mi, 0x22222222UL, 24),
                         IsMovValueToStack(X86::MOV32mi, 0x11111111UL, 28),
-                        IsMovValueFromStack(X86::VMOVDQU32Z256rm, X86::YMM0),
+                        IsMovValueFromStack(X86::VMOVDQUYrm, X86::YMM0),
                         IsStackDeallocate(32)}));
 }
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/114768