[WebAssembly] Revise the strategy for inline asm.

Previously, an "r" constraint would mean the compiler provides a value
on WebAssembly's operand stack. This was tricky to use properly,
particularly since it isn't possible to declare a new local from within
an inline asm string.

With this patch, "r" provides the value in a WebAssembly local, and the
local index is provided to the inline asm string. This requires inline
asm to use get_local and set_local to read the register. This does
potentially result in larger code size, however inline asm should
hopefully be quite rare in WebAssembly.

This also means that the "m" constraint can no longer be supported, as
WebAssembly has nothing like a "memory operand" that includes an
implicit get_local.

This fixes PR34599 for the wasm32-unknown-unknown-wasm target (though
not for the ELF target).

llvm-svn: 317707

1 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
index 41249117ae0..e2edb924d4d 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
@@ -294,6 +294,17 @@ bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
 
         unsigned OldReg = MO.getReg();
 
+        // Inline asm may have a def in the middle of the operands. Our contract
+        // with inline asm register operands is to provide local indices as
+        // immediates.
+        if (MO.isDef()) {
+          assert(MI.getOpcode() == TargetOpcode::INLINEASM);
+          unsigned LocalId = getLocalId(Reg2Local, CurLocal, OldReg);
+          MRI.removeRegOperandFromUseList(&MO);
+          MO = MachineOperand::CreateImm(LocalId);
+          continue;
+        }
+
         // If we see a stackified register, prepare to insert subsequent
         // get_locals before the start of its tree.
         if (MFI.isVRegStackified(OldReg)) {
@@ -301,6 +312,15 @@ bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
           continue;
         }
 
+        // Our contract with inline asm register operands is to provide local
+        // indices as immediates.
+        if (MI.getOpcode() == TargetOpcode::INLINEASM) {
+          unsigned LocalId = getLocalId(Reg2Local, CurLocal, OldReg);
+          MRI.removeRegOperandFromUseList(&MO);
+          MO = MachineOperand::CreateImm(LocalId);
+          continue;
+        }
+
         // Insert a get_local.
         unsigned LocalId = getLocalId(Reg2Local, CurLocal, OldReg);
         const TargetRegisterClass *RC = MRI.getRegClass(OldReg);