[PATCH] D56094: [WebAssembly] Fix stack pointer store check in RegStackify

[Heejin Ahn via Phabricator via llvm-commits]

aheejin created this revision.
aheejin added reviewers: sbc100, sunfish.
Herald added subscribers: llvm-commits, jgravelle-google, dschuff.

We now use __stack_pointer global and get_global/set_global instruction.
This fixes the checking routine for stack_pointer writes accordingly.

This also fixes the existing __stack_pointer test in reg-stackify.ll:
That test used to pass not because of __stack_pointer clashes but
because the function `stackpointer_callee` was not marked as `readnone`,
so it was assumed to possibly write to memory arbitraily, and
`set_global` instruction was marked as `mayStore` in the .td definition,
so they were identified as intervening writes. After we added `readnone`
to its attribute, this test fails without this patch.


Repository:
  rL LLVM

https://reviews.llvm.org/D56094

Files:
  lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
  test/CodeGen/WebAssembly/reg-stackify.ll


Index: test/CodeGen/WebAssembly/reg-stackify.ll
===================================================================
--- test/CodeGen/WebAssembly/reg-stackify.ll
+++ test/CodeGen/WebAssembly/reg-stackify.ll
@@ -634,7 +634,7 @@
 ; NOREGS-LABEL: stackpointer_dependency:
 ; NOREGS:      call stackpointer_callee at FUNCTION
 ; NOREGS:      set_global __stack_pointer
-declare i32 @stackpointer_callee(i8* readnone, i8* readnone)
+declare i32 @stackpointer_callee(i8* readnone, i8* readnone) nounwind readnone
 declare i8* @llvm.frameaddress(i32)
 define i32 @stackpointer_dependency(i8* readnone) {
   %2 = tail call i8* @llvm.frameaddress(i32 0)
Index: lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
===================================================================
--- lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
+++ lib/Target/WebAssembly/WebAssemblyRegStackify.cpp
@@ -181,19 +181,6 @@
   // Check for stores.
   if (MI.mayStore()) {
     Write = true;
-
-    // Check for stores to __stack_pointer.
-    for (auto MMO : MI.memoperands()) {
-      const MachinePointerInfo &MPI = MMO->getPointerInfo();
-      if (MPI.V.is<const PseudoSourceValue *>()) {
-        auto PSV = MPI.V.get<const PseudoSourceValue *>();
-        if (const ExternalSymbolPseudoSourceValue *EPSV =
-                dyn_cast<ExternalSymbolPseudoSourceValue>(PSV))
-          if (StringRef(EPSV->getSymbol()) == "__stack_pointer") {
-            StackPointer = true;
-          }
-      }
-    }
   } else if (MI.hasOrderedMemoryRef()) {
     switch (MI.getOpcode()) {
     case WebAssembly::DIV_S_I32:
@@ -258,6 +245,11 @@
     }
   }
 
+  // Check for stores to __stack_pointer global.
+  if (MI.getOpcode() == WebAssembly::SET_GLOBAL_I32 &&
+      strcmp(MI.getOperand(0).getSymbolName(), "__stack_pointer") == 0)
+    StackPointer = true;
+
   // Analyze calls.
   if (MI.isCall()) {
     unsigned CalleeOpNo = WebAssembly::getCalleeOpNo(MI);


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