[PATCH] D149191: [CodeGen][MachineLastInstrsCleanup] don't hoist loads above INLINEASM

[Nick Desaulniers via Phabricator via llvm-commits]

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If an inline asm stores to memory or otherwise has side-effects, it's
not safe to hoist loads across it.

This is causing a boot failure on linux-4.19.y branches of the LTS Linux
kernel for ARCH=arm64 with CONFIG_RANDOMIZE_BASE=y (KASLR) and
CONFIG_UNMAP_KERNEL_AT_EL0=y (KPTI).

Fixes: D123394 <https://reviews.llvm.org/D123394>
Link: https://github.com/ClangBuiltLinux/linux/issues/1837


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D149191

Files:
  llvm/lib/CodeGen/MachineLateInstrsCleanup.cpp
  llvm/test/CodeGen/X86/machine-latecleanup-inlineasm.mir


Index: llvm/test/CodeGen/X86/machine-latecleanup-inlineasm.mir
===================================================================
--- llvm/test/CodeGen/X86/machine-latecleanup-inlineasm.mir
+++ llvm/test/CodeGen/X86/machine-latecleanup-inlineasm.mir
@@ -89,8 +89,9 @@
   ; CHECK-NEXT: {{  $}}
   ; CHECK-NEXT:   $rsp = frame-setup SUB64ri8 $rsp, 24, implicit-def dead $eflags
   ; CHECK-NEXT:   renamable $rax = LOAD_STACK_GUARD :: (dereferenceable invariant load (s64) from @__stack_chk_guard)
-  ; CHECK-NEXT:   MOV64mr $rsp, 1, $noreg, 16, $noreg, renamable $rax :: (volatile store (s64) into %stack.0.StackGuardSlot)
+  ; CHECK-NEXT:   MOV64mr $rsp, 1, $noreg, 16, $noreg, killed renamable $rax :: (volatile store (s64) into %stack.0.StackGuardSlot)
   ; CHECK-NEXT:   INLINEASM &"", 25 /* sideeffect mayload maystore attdialect */
+  ; CHECK-NEXT:   renamable $rax = LOAD_STACK_GUARD :: (dereferenceable invariant load (s64) from @__stack_chk_guard)
   ; CHECK-NEXT:   CMP64rm killed renamable $rax, $rsp, 1, $noreg, 16, $noreg, implicit-def $eflags :: (volatile load (s64) from %stack.0.StackGuardSlot)
   ; CHECK-NEXT:   JCC_1 %bb.1, 5, implicit killed $eflags
   ; CHECK-NEXT:   JMP_1 %bb.2
@@ -103,6 +104,7 @@
   ; CHECK-NEXT: bb.2.entry:
   ; CHECK-NEXT:   $rsp = frame-destroy ADD64ri8 $rsp, 24, implicit-def dead $eflags
   ; CHECK-NEXT:   RET 0
+  ; CHECK-BLANK: {{  $}}
   bb.0.entry:
     successors: %bb.2(0x7ffff800), %bb.1(0x00000800)
 
Index: llvm/lib/CodeGen/MachineLateInstrsCleanup.cpp
===================================================================
--- llvm/lib/CodeGen/MachineLateInstrsCleanup.cpp
+++ llvm/lib/CodeGen/MachineLateInstrsCleanup.cpp
@@ -196,9 +196,11 @@
   const TargetRegisterInfo *TRI = MF->getSubtarget().getRegisterInfo();
   Register FrameReg = TRI->getFrameRegister(*MF);
   for (MachineInstr &MI : llvm::make_early_inc_range(*MBB)) {
-    // If FrameReg is modified, no previous load-address instructions (using
-    // it) are valid.
-    if (MI.modifiesRegister(FrameReg, TRI)) {
+    // If FrameReg is modified or we have an inline asm that may store or have
+    // other side effects, no previous load-address instructions (using it) are
+    // valid.
+    if (MI.modifiesRegister(FrameReg, TRI) ||
+        (MI.isInlineAsm() && (MI.hasUnmodeledSideEffects() || MI.mayStore()))) {
       MBBDefs.clear();
       continue;
     }


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