[llvm] ef102b4 - [MachineLICM] Don't allow hoisting invariant loads across mem barrier. (#116987)
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Thu Nov 21 02:25:08 PST 2024
Author: Florian Hahn
Date: 2024-11-21T10:25:04Z
New Revision: ef102b4a6333a304e36dc623d5381257a7ef1ed6
URL: https://github.com/llvm/llvm-project/commit/ef102b4a6333a304e36dc623d5381257a7ef1ed6
DIFF: https://github.com/llvm/llvm-project/commit/ef102b4a6333a304e36dc623d5381257a7ef1ed6.diff
LOG: [MachineLICM] Don't allow hoisting invariant loads across mem barrier. (#116987)
The improvements in 63917e1 / #70796 do not check for memory
barriers/unmodelled sideeffects, which means we may incorrectly hoist
loads across memory barriers.
Fix this by checking any machine instruction in the loop is a load-fold
barrier.
PR: https://github.com/llvm/llvm-project/pull/116987
Added:
Modified:
llvm/lib/CodeGen/MachineLICM.cpp
llvm/test/CodeGen/AArch64/machine-licm-hoist-load.ll
llvm/test/CodeGen/Mips/lcb5.ll
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/MachineLICM.cpp b/llvm/lib/CodeGen/MachineLICM.cpp
index 94cbbf7834c626..d21059189b1844 100644
--- a/llvm/lib/CodeGen/MachineLICM.cpp
+++ b/llvm/lib/CodeGen/MachineLICM.cpp
@@ -1501,7 +1501,7 @@ void MachineLICMImpl::InitializeLoadsHoistableLoops() {
if (!AllowedToHoistLoads[Loop])
continue;
for (auto &MI : *MBB) {
- if (!MI.mayStore() && !MI.isCall() &&
+ if (!MI.isLoadFoldBarrier() && !MI.mayStore() && !MI.isCall() &&
!(MI.mayLoad() && MI.hasOrderedMemoryRef()))
continue;
for (MachineLoop *L = Loop; L != nullptr; L = L->getParentLoop())
diff --git a/llvm/test/CodeGen/AArch64/machine-licm-hoist-load.ll b/llvm/test/CodeGen/AArch64/machine-licm-hoist-load.ll
index 932a5af264a000..17f8263560430d 100644
--- a/llvm/test/CodeGen/AArch64/machine-licm-hoist-load.ll
+++ b/llvm/test/CodeGen/AArch64/machine-licm-hoist-load.ll
@@ -499,16 +499,16 @@ for.exit: ; preds = %for.body
@a = external local_unnamed_addr global i32, align 4
-; FIXME: Load hoisted out of the loop across memory barriers.
+; Make sure the load is not hoisted out of the loop across memory barriers.
define i32 @load_between_memory_barriers() {
; CHECK-LABEL: load_between_memory_barriers:
; CHECK: // %bb.0:
; CHECK-NEXT: adrp x8, :got:a
; CHECK-NEXT: ldr x8, [x8, :got_lo12:a]
-; CHECK-NEXT: ldr w0, [x8]
; CHECK-NEXT: .LBB8_1: // %loop
; CHECK-NEXT: // =>This Inner Loop Header: Depth=1
; CHECK-NEXT: //MEMBARRIER
+; CHECK-NEXT: ldr w0, [x8]
; CHECK-NEXT: //MEMBARRIER
; CHECK-NEXT: cbz w0, .LBB8_1
; CHECK-NEXT: // %bb.2: // %exit
diff --git a/llvm/test/CodeGen/Mips/lcb5.ll b/llvm/test/CodeGen/Mips/lcb5.ll
index f320f6fc5660ce..bb059f1ee8453e 100644
--- a/llvm/test/CodeGen/Mips/lcb5.ll
+++ b/llvm/test/CodeGen/Mips/lcb5.ll
@@ -186,7 +186,7 @@ if.end: ; preds = %if.then, %entry
}
; ci: .ent z3
-; ci: bteqz $BB6_3
+; ci: bteqz $BB6_2
; ci: .end z3
; Function Attrs: nounwind optsize
@@ -210,7 +210,7 @@ if.end: ; preds = %if.then, %entry
; ci: .ent z4
; ci: btnez $BB7_1 # 16 bit inst
-; ci: jal $BB7_3 # branch
+; ci: jal $BB7_2 # branch
; ci: nop
; ci: $BB7_1:
; ci: .p2align 2
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