[llvm] RegisterCoalescer: Relax assert for super register def rematerialization (PR #69088)
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Sat Oct 14 19:50:17 PDT 2023
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-backend-x86
Author: Matt Arsenault (arsenm)
<details>
<summary>Changes</summary>
Depending on the uses, the super register def added when coalescing SUBREG_TO_REG may have been reduced to some set of used subregisters so we may not just see a simple super register reference.
---
Full diff: https://github.com/llvm/llvm-project/pull/69088.diff
3 Files Affected:
- (modified) llvm/lib/CodeGen/RegisterCoalescer.cpp (+10-4)
- (added) llvm/test/CodeGen/X86/coalescer-implicit-def-regression-imp-operand-assert.mir (+39)
- (added) llvm/test/CodeGen/X86/coalescer-implicit-def-regression.mir (+91)
``````````diff
diff --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index 7e5ce300370c92b..78c5ccde5d626a6 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -1415,6 +1415,9 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
// from SUBREG_TO_REG, such as:
// $edi = MOV32r0 implicit-def dead $eflags, implicit-def $rdi
// undef %0.sub_32bit = MOV32r0 implicit-def dead $eflags, implicit-def %0
+ //
+ // The implicit-def of the super register may have been reduced to
+ // subregisters depending on the uses.
bool NewMIDefinesFullReg = false;
@@ -1432,12 +1435,15 @@ bool RegisterCoalescer::reMaterializeTrivialDef(const CoalescerPair &CP,
assert(MO.isImplicit() && MO.getReg().isPhysical() &&
(MO.isDead() ||
(DefSubIdx &&
- (TRI->getSubReg(MO.getReg(), DefSubIdx) ==
- MCRegister((unsigned)NewMI.getOperand(0).getReg())))));
+ ((TRI->getSubReg(MO.getReg(), DefSubIdx) ==
+ MCRegister((unsigned)NewMI.getOperand(0).getReg())) ||
+ TRI->isSubRegisterEq(NewMI.getOperand(0).getReg(), MO.getReg())
+ )))
+ );
NewMIImplDefs.push_back(MO.getReg().asMCReg());
} else {
- assert(MO.getReg() == NewMI.getOperand(0).getReg() &&
- MO.getSubReg() == 0);
+ assert(MO.getReg() == NewMI.getOperand(0).getReg());
+
// We're only expecting another def of the main output, so the range
// should get updated with the regular output range.
//
diff --git a/llvm/test/CodeGen/X86/coalescer-implicit-def-regression-imp-operand-assert.mir b/llvm/test/CodeGen/X86/coalescer-implicit-def-regression-imp-operand-assert.mir
new file mode 100644
index 000000000000000..14220ee01131f9a
--- /dev/null
+++ b/llvm/test/CodeGen/X86/coalescer-implicit-def-regression-imp-operand-assert.mir
@@ -0,0 +1,39 @@
+# RUN: llc -mtriple=x86_64-unknown-linux-gnu -run-pass=register-coalescer -o - %s
+---
+name: rematerialize_subreg_to_reg_added_impdef_1
+tracksRegLiveness: true
+body: |
+ bb.0:
+ successors: %bb.1(0x2aaaaaab), %bb.2(0x55555555)
+ liveins: $edi
+
+ %0:gr32 = MOV32r0 implicit-def dead $eflags
+ %1:gr8 = COPY %0.sub_8bit
+ %2:gr64 = SUBREG_TO_REG 0, killed %0, %subreg.sub_32bit
+ JCC_1 %bb.2, 5, implicit killed undef $eflags
+
+ bb.1:
+ successors: %bb.3(0x80000000)
+
+ JMP_1 %bb.3
+
+ bb.2:
+ successors: %bb.3(0x80000000)
+
+ %5:gr64 = IMPLICIT_DEF
+ %2:gr64 = COPY killed %5
+
+ bb.3:
+ successors: %bb.4(0x30000000), %bb.5(0x50000000)
+
+ JCC_1 %bb.5, 5, implicit killed undef $eflags
+
+ bb.4:
+ $al = COPY killed %1
+ RET 0, killed undef $al
+
+ bb.5:
+ MOV64mr undef $noreg, 1, undef $noreg, 0, undef $noreg, killed %2 :: (store (s64))
+ RET 0, killed undef $al
+
+...
diff --git a/llvm/test/CodeGen/X86/coalescer-implicit-def-regression.mir b/llvm/test/CodeGen/X86/coalescer-implicit-def-regression.mir
new file mode 100644
index 000000000000000..722d9b60841a278
--- /dev/null
+++ b/llvm/test/CodeGen/X86/coalescer-implicit-def-regression.mir
@@ -0,0 +1,91 @@
+# RUN: llc -mtriple=x86_64-unknown-linux-gnu -run-pass=register-coalescer -o - %s
+
+# An implicit-def will be added to SUBREG_TO_REG during coalescing
+---
+name: rematerialize_subreg_to_reg_added_impdef_0
+tracksRegLiveness: true
+body: |
+ bb.0:
+ successors: %bb.1(0x2aaaaaab), %bb.2(0x55555555)
+ liveins: $edi
+
+ %0:gr32 = MOV32r0 implicit-def dead $eflags
+ %1:gr8 = COPY %0.sub_8bit
+ %2:gr64 = SUBREG_TO_REG 0, killed %0, %subreg.sub_32bit
+ JCC_1 %bb.2, 5, implicit killed undef $eflags
+
+ bb.1:
+ %4:gr8 = COPY %1
+ %5:gr8 = COPY killed undef %1
+ JMP_1 %bb.5
+
+ bb.2:
+ %6:gr64 = IMPLICIT_DEF
+ %2:gr64 = COPY killed %6
+ %5:gr8 = MOV8ri 1
+
+ bb.5:
+ successors: %bb.6(0x30000000), %bb.7(0x50000000)
+
+ TEST8rr killed undef %5, %5, implicit-def $eflags
+ JCC_1 %bb.7, 5, implicit killed undef $eflags
+
+ bb.6:
+ $al = COPY killed %1
+ RET 0, killed undef $al
+
+ bb.7:
+ MOV64mr undef $noreg, 1, undef $noreg, 0, undef $noreg, killed %2 :: (store (s64))
+ RET 0, killed undef $al
+
+...
+
+
+# Reduced version of previous with the SUBREG_TO_REG already folded
+# away.
+#
+# The mov32r0 defines a subregister and has an implicit-def of the
+# super register. After coalescing, the full register implicit def of
+# %2 becomes a different subregister def.
+
+---
+name: rematerialize_subreg_to_reg_coalesces_to_subreg_impdef
+tracksRegLiveness: true
+body: |
+ bb.0:
+ successors: %bb.1(0x2aaaaaab), %bb.2(0x55555555)
+ liveins: $edi
+
+ undef %2.sub_32bit:gr64_with_sub_8bit = MOV32r0 implicit-def dead $eflags, implicit-def %2
+ %1:gr8 = COPY %2.sub_8bit
+ JCC_1 %bb.2, 5, implicit killed undef $eflags
+
+ bb.1:
+ successors: %bb.3(0x80000000)
+
+ dead %3:gr8 = COPY %1
+ %4:gr8 = COPY undef %1
+ JMP_1 %bb.3
+
+ bb.2:
+ successors: %bb.3(0x80000000)
+
+ %5:gr64 = IMPLICIT_DEF
+ %2:gr64_with_sub_8bit = COPY %5
+ %4:gr8 = MOV8ri 1
+
+ bb.3:
+ successors: %bb.4(0x30000000), %bb.5(0x50000000)
+
+ TEST8rr undef %4, %4, implicit-def $eflags
+ JCC_1 %bb.5, 5, implicit killed undef $eflags
+
+ bb.4:
+ $al = COPY %1
+ RET 0, killed undef $al
+
+ bb.5:
+ MOV64mr undef $noreg, 1, undef $noreg, 0, undef $noreg, %2 :: (store (s64))
+ RET 0, killed undef $al
+
+...
``````````
</details>
https://github.com/llvm/llvm-project/pull/69088
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