[llvm] 51b13a7 - [gvn] CSE gc.relocates based on meaning, not spelling

[Philip Reames via llvm-commits]

Author: Philip Reames
Date: 2021-03-05T10:16:12-08:00
New Revision: 51b13a7ea0b9123a405a51241763ed388d68a46f

URL: https://github.com/llvm/llvm-project/commit/51b13a7ea0b9123a405a51241763ed388d68a46f
DIFF: https://github.com/llvm/llvm-project/commit/51b13a7ea0b9123a405a51241763ed388d68a46f.diff

LOG: [gvn] CSE gc.relocates based on meaning, not spelling

The last two operands to a gc.relocate represent indices into the associated gc.statepoint's gc bundle list. (Effectively, gc.relocates are projections from the gc.statepoints multiple return values.)

We can use this to recognize when two gc.relocates are equivalent (and can be CSEd), even when the indices are non-equal. This is particular useful when considering a chain of multiple statepoints as it lets us eliminate all duplicate gc.relocates in a single pass.

Differential Revision: https://reviews.llvm.org/D97974

(Note: Part of the reviewed change was split and landed as f352463a)

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/GVN.cpp
    llvm/test/Transforms/GVN/gc_relocate.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/GVN.cpp b/llvm/lib/Transforms/Scalar/GVN.cpp
index 24491d37616b..30b947f6ef3d 100644
--- a/llvm/lib/Transforms/Scalar/GVN.cpp
+++ b/llvm/lib/Transforms/Scalar/GVN.cpp
@@ -62,6 +62,7 @@
 #include "llvm/IR/Operator.h"
 #include "llvm/IR/PassManager.h"
 #include "llvm/IR/PatternMatch.h"
+#include "llvm/IR/Statepoint.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/Use.h"
 #include "llvm/IR/Value.h"
@@ -289,8 +290,17 @@ GVN::Expression GVN::ValueTable::createExpr(Instruction *I) {
   Expression e;
   e.type = I->getType();
   e.opcode = I->getOpcode();
-  for (Use &Op : I->operands())
-    e.varargs.push_back(lookupOrAdd(Op));
+  if (const GCRelocateInst *GCR = dyn_cast<GCRelocateInst>(I)) {
+    // gc.relocate is 'special' call: its second and third operands are
+    // not real values, but indices into statepoint's argument list.
+    // Use the refered to values for purposes of identity.
+    e.varargs.push_back(lookupOrAdd(GCR->getOperand(0)));
+    e.varargs.push_back(lookupOrAdd(GCR->getBasePtr()));
+    e.varargs.push_back(lookupOrAdd(GCR->getDerivedPtr()));
+  } else {
+    for (Use &Op : I->operands())
+      e.varargs.push_back(lookupOrAdd(Op));
+  }
   if (I->isCommutative()) {
     // Ensure that commutative instructions that only 
diff er by a permutation
     // of their operands get the same value number by sorting the operand value

diff  --git a/llvm/test/Transforms/GVN/gc_relocate.ll b/llvm/test/Transforms/GVN/gc_relocate.ll
index f67db73fdd17..bd279bdf42bb 100644
--- a/llvm/test/Transforms/GVN/gc_relocate.ll
+++ b/llvm/test/Transforms/GVN/gc_relocate.ll
@@ -49,14 +49,10 @@ define i1 @test_call(i32 addrspace(1)* %in) gc "statepoint-example" {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[SAFEPOINT_TOKEN:%.*]] = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0) [ "gc-live"(i32 addrspace(1)* [[IN:%.*]], i32 addrspace(1)* [[IN]]) ]
 ; CHECK-NEXT:    [[BASE:%.*]] = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token [[SAFEPOINT_TOKEN]], i32 0, i32 0)
-; CHECK-NEXT:    [[DERIVED:%.*]] = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token [[SAFEPOINT_TOKEN]], i32 0, i32 1)
-; CHECK-NEXT:    [[SAFEPOINT_TOKEN2:%.*]] = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0) [ "gc-live"(i32 addrspace(1)* [[BASE]], i32 addrspace(1)* [[DERIVED]]) ]
+; CHECK-NEXT:    [[SAFEPOINT_TOKEN2:%.*]] = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0) [ "gc-live"(i32 addrspace(1)* [[BASE]], i32 addrspace(1)* [[BASE]]) ]
 ; CHECK-NEXT:    [[BASE_RELOC:%.*]] = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token [[SAFEPOINT_TOKEN2]], i32 0, i32 0)
-; CHECK-NEXT:    [[DERIVED_RELOC:%.*]] = call i32 addrspace(1)* @llvm.experimental.gc.relocate.p1i32(token [[SAFEPOINT_TOKEN2]], i32 0, i32 1)
 ; CHECK-NEXT:    [[CMP1:%.*]] = icmp eq i32 addrspace(1)* [[BASE_RELOC]], null
-; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i32 addrspace(1)* [[DERIVED_RELOC]], null
-; CHECK-NEXT:    [[CMP:%.*]] = and i1 [[CMP1]], [[CMP2]]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    ret i1 [[CMP1]]
 ;
 entry:
   %safepoint_token = call token (i64, i32, void ()*, i32, i32, ...) @llvm.experimental.gc.statepoint.p0f_isVoidf(i64 0, i32 0, void ()* @func, i32 0, i32 0, i32 0, i32 0) ["gc-live"(i32 addrspace(1)* %in, i32 addrspace(1)* %in)]