[PATCH] D124406: [X86] Use indirect addressing for high 2GB of x32 address space

[Harald van Dijk via Phabricator via llvm-commits]

hvdijk updated this revision to Diff 557167.
hvdijk added a comment.

Rebased.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D124406/new/

https://reviews.llvm.org/D124406

Files:
  llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
  llvm/test/CodeGen/X86/large-constants-x32.ll


Index: llvm/test/CodeGen/X86/large-constants-x32.ll
===================================================================
--- llvm/test/CodeGen/X86/large-constants-x32.ll
+++ llvm/test/CodeGen/X86/large-constants-x32.ll
@@ -4,12 +4,16 @@
 define void @constant_expressions() {
 ; CHECK-LABEL: constant_expressions:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    movl -289477652, %eax
-; CHECK-NEXT:    movl -289477644, %ecx
-; CHECK-NEXT:    addl -289477648, %eax
-; CHECK-NEXT:    addl -289477636, %ecx
-; CHECK-NEXT:    addl %eax, %ecx
-; CHECK-NEXT:    movl %ecx, -289477652
+; CHECK-NEXT:    movl $-289477652, %eax # imm = 0xEEBEEBEC
+; CHECK-NEXT:    movl (%eax), %ecx
+; CHECK-NEXT:    movl $-289477644, %edx # imm = 0xEEBEEBF4
+; CHECK-NEXT:    movl (%edx), %edx
+; CHECK-NEXT:    movl $-289477648, %esi # imm = 0xEEBEEBF0
+; CHECK-NEXT:    addl (%esi), %ecx
+; CHECK-NEXT:    movl $-289477636, %esi # imm = 0xEEBEEBFC
+; CHECK-NEXT:    addl (%esi), %edx
+; CHECK-NEXT:    addl %ecx, %edx
+; CHECK-NEXT:    movl %edx, (%eax)
 ; CHECK-NEXT:    retq
 entry:
   %0 = load i32, i32* inttoptr (i32 add (i32 -289477652, i32 0) to i32*)
@@ -27,12 +31,16 @@
 define void @constant_expressions2() {
 ; CHECK-LABEL: constant_expressions2:
 ; CHECK:       # %bb.0: # %entry
-; CHECK-NEXT:    movl -289477652, %eax
-; CHECK-NEXT:    movl -289477644, %ecx
-; CHECK-NEXT:    addl -289477648, %eax
-; CHECK-NEXT:    addl -289477640, %ecx
-; CHECK-NEXT:    addl %eax, %ecx
-; CHECK-NEXT:    movl %ecx, -289477652
+; CHECK-NEXT:    movl $-289477652, %eax # imm = 0xEEBEEBEC
+; CHECK-NEXT:    movl (%eax), %ecx
+; CHECK-NEXT:    movl $-289477644, %edx # imm = 0xEEBEEBF4
+; CHECK-NEXT:    movl (%edx), %edx
+; CHECK-NEXT:    movl $-289477648, %esi # imm = 0xEEBEEBF0
+; CHECK-NEXT:    addl (%esi), %ecx
+; CHECK-NEXT:    movl $-289477640, %esi # imm = 0xEEBEEBF8
+; CHECK-NEXT:    addl (%esi), %edx
+; CHECK-NEXT:    addl %ecx, %edx
+; CHECK-NEXT:    movl %edx, (%eax)
 ; CHECK-NEXT:    retq
 entry:
   %0 = load i32, i32* inttoptr (i32 -289477652 to i32*)
Index: llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -1699,10 +1699,28 @@
     if (AM.BaseType == X86ISelAddressMode::FrameIndexBase &&
         !isDispSafeForFrameIndex(Val))
       return true;
+    // In ILP32 (x32) mode, pointers are 32 bits and need to be zero-extended to
+    // 64 bits. Instructions with 32-bit register addresses perform this zero
+    // extension for us and we can safely ignore the high bits of Offset.
+    // Instructions with only a 32-bit immediate address do not, though: they
+    // sign extend instead. This means only address the low 2GB of address space
+    // is directly addressable, we need indirect addressing for the high 2GB of
+    // address space.
+    // TODO: Some of the earlier checks may be relaxed for ILP32 mode as the
+    // implicit zero extension of instructions would cover up any problem.
+    // However, we have asserts elsewhere that get triggered if we do, so keep
+    // the checks for now.
+    // TODO: We would actually be able to accept these, as well as the same
+    // addresses in LP64 mode, by adding the EIZ pseudo-register as an operand
+    // to get an address size override to be emitted. However, this
+    // pseudo-register is not part of any register class and therefore causes
+    // MIR verification to fail.
+    if (Subtarget->isTarget64BitILP32() && !isUInt<31>(Val) &&
+        !AM.hasBaseOrIndexReg())
+      return true;
   }
   AM.Disp = Val;
   return false;
-
 }
 
 bool X86DAGToDAGISel::matchLoadInAddress(LoadSDNode *N, X86ISelAddressMode &AM,


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