Explicitly define df register (#263)

Now that llvm-exegesis has support for explicitly setting the df register, we should explicitly define df rather than eflags/rflags when something in the block uses df. This fixes a MC verification error when using the loop snippet repetitor due to implicitly defined registers not being set as live-ins.
google · Nov 18, 2024 · dc456ad · dc456ad
1 parent 4c9d7b7
commit dc456ad
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Showing 4 changed files with 5 additions and 9 deletions.
diff --git a/gematria/datasets/basic_block_utils.cc b/gematria/datasets/basic_block_utils.cc
@@ -33,12 +33,6 @@ namespace gematria {
 
 unsigned getSuperRegister(unsigned OriginalRegister,
                           const MCRegisterInfo &RegisterInfo) {
-  // Sections of EFLAGS that are explicitly modeled by LLVM as separate
-  // registers should all return eflags.
-  if (OriginalRegister == X86::EFLAGS || OriginalRegister == X86::DF) {
-    return X86::EFLAGS;
-  }
-
   // We should be able to get the super register by getting an iterator from
   // RegisterInfo and getting the back, but this always returns a value of
   // zero.

diff --git a/gematria/datasets/basic_block_utils_test.cc b/gematria/datasets/basic_block_utils_test.cc
@@ -193,8 +193,7 @@ TEST_F(BasicBlockUtilsTest, MovsqImplicitDfUsesEflags) {
   std::vector<unsigned> UsedRegisters = getUsedRegs(R"asm(
     movsq
   )asm");
-  EXPECT_THAT(UsedRegisters,
-              UnorderedElementsAre(X86::RSI, X86::RDI, X86::EFLAGS));
+  EXPECT_THAT(UsedRegisters, UnorderedElementsAre(X86::RSI, X86::RDI, X86::DF));
 }
 
 TEST_F(BasicBlockUtilsTest, UnusedGPRegisterSingleInstruction) {

diff --git a/gematria/datasets/find_accessed_addrs_exegesis.cc b/gematria/datasets/find_accessed_addrs_exegesis.cc
@@ -179,7 +179,7 @@ Expected<ExecutionAnnotations> ExegesisAnnotator::findAccessedAddrs(
       RegVal.Value = APInt(32, kInitialRegVal);
       NewRegisterValue->set_register_value(kInitialRegVal);
     } else if (RegisterIndex == X86::EFLAGS || RegisterIndex == X86::MXCSR ||
-               RegisterIndex == X86::FPCW) {
+               RegisterIndex == X86::FPCW || RegisterIndex == X86::DF) {
       RegVal.Value = APInt(32, 0);
       NewRegisterValue->set_register_value(0);
     } else if (MRI.getRegClass(X86::RFP32RegClassID).contains(RegisterIndex)) {

diff --git a/gematria/datasets/find_accessed_addrs_exegesis_test.cc b/gematria/datasets/find_accessed_addrs_exegesis_test.cc
@@ -174,6 +174,9 @@ TEST_F(FindAccessedAddrsExegesisTest, DFRegister) {
     movsq
   )asm");
   ASSERT_TRUE(static_cast<bool>(AddrsOrErr));
+  EXPECT_THAT(AddrsOrErr->initial_registers(),
+              Contains(Property("register_name",
+                                &RegisterAndValue::register_name, "DF")));
 }
 
 // Test that we can annotate snippets using various different register