[PATCH] D93931: [X86] Don't fold negative offset into 32-bit absolute address (e.g. movl $foo-1, %eax)
Fangrui Song via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Wed Dec 30 09:24:13 PST 2020
MaskRay updated this revision to Diff 314127.
MaskRay edited the summary of this revision.
MaskRay added a comment.
Simplify
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D93931/new/
https://reviews.llvm.org/D93931
Files:
llvm/lib/Target/X86/X86ISelLowering.cpp
llvm/lib/Target/X86/X86ISelLowering.h
llvm/test/CodeGen/X86/fold-add.ll
Index: llvm/test/CodeGen/X86/fold-add.ll
===================================================================
--- llvm/test/CodeGen/X86/fold-add.ll
+++ llvm/test/CodeGen/X86/fold-add.ll
@@ -54,10 +54,12 @@
ret i64 add (i64 ptrtoint (i32* @foo to i64), i64 1701208431)
}
+;; Test we don't emit movl foo-1, %eax. ELF R_X86_64_32 does not allow
+;; a negative value.
define dso_local i64 @neg_1() #0 {
; CHECK-LABEL: neg_1:
; CHECK: # %bb.0:
-; STATIC-NEXT: movl $foo-1, %eax
+; STATIC-NEXT: leaq foo-1(%rip), %rax
; PIC-NEXT: leaq foo-1(%rip), %rax
; MSTATIC-NEXT: movabsq $foo, %rax
; MSTATIC-NEXT: decq %rax
@@ -71,7 +73,7 @@
define dso_local i64 @neg_0x80000000() #0 {
; CHECK-LABEL: neg_0x80000000:
; CHECK: # %bb.0:
-; STATIC-NEXT: movl $foo-2147483648, %eax
+; STATIC-NEXT: leaq foo-2147483648(%rip), %rax
; PIC-NEXT: leaq foo-2147483648(%rip), %rax
; MSTATIC-NEXT: movabsq $foo, %rax
; MSTATIC-NEXT: addq $-2147483648, %rax
Index: llvm/lib/Target/X86/X86ISelLowering.h
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.h
+++ llvm/lib/Target/X86/X86ISelLowering.h
@@ -855,7 +855,7 @@
/// Returns true of the given offset can be
/// fit into displacement field of the instruction.
bool isOffsetSuitableForCodeModel(int64_t Offset, CodeModel::Model M,
- bool hasSymbolicDisplacement = true);
+ bool hasSymbolicDisplacement);
/// Determines whether the callee is required to pop its
/// own arguments. Callee pop is necessary to support tail calls.
Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -4889,7 +4889,7 @@
// For small code model we assume that latest object is 16MB before end of 31
// bits boundary. We may also accept pretty large negative constants knowing
// that all objects are in the positive half of address space.
- if (M == CodeModel::Small && Offset < 16*1024*1024)
+ if (M == CodeModel::Small && Offset < 16 * 1024 * 1024)
return true;
// For kernel code model we know that all object resist in the negative half
@@ -19102,9 +19102,13 @@
if (GV) {
// Create a target global address if this is a global. If possible, fold the
// offset into the global address reference. Otherwise, ADD it on later.
+ // Suppress the folding if Offset is negative: movl foo-1, %eax is not
+ // allowed because if the address of foo is 0, the ELF R_X86_64_32
+ // relocation will fail to link because the value cannot be negative.
int64_t GlobalOffset = 0;
if (OpFlags == X86II::MO_NO_FLAG &&
- X86::isOffsetSuitableForCodeModel(Offset, M)) {
+ Offset >= 0 &&
+ X86::isOffsetSuitableForCodeModel(Offset, M, true)) {
std::swap(GlobalOffset, Offset);
}
Result = DAG.getTargetGlobalAddress(GV, dl, PtrVT, GlobalOffset, OpFlags);
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