[llvm] e48916f - [ARM][ConstantIslands] Correct MinNoSplitDisp calculation (#114590)
via llvm-commits
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Sat Dec 14 10:14:53 PST 2024
Author: pzhengqc
Date: 2024-12-14T10:14:50-08:00
New Revision: e48916f615e0ad2b994b2b785d4fe1b8a98bc322
URL: https://github.com/llvm/llvm-project/commit/e48916f615e0ad2b994b2b785d4fe1b8a98bc322
DIFF: https://github.com/llvm/llvm-project/commit/e48916f615e0ad2b994b2b785d4fe1b8a98bc322.diff
LOG: [ARM][ConstantIslands] Correct MinNoSplitDisp calculation (#114590)
MinNoSplitDisp was first introduced in D16890 to handle cases where the
ConstantIslands pass fails to converge in the presence of big basic
blocks. However, the computation of the variable seems to be wrong as it
currently computes the offset immediately following UserBB. In other
words, it represents the distance from the beginning of the function to
the end of UserBB. The distance from the beginning of the function does
not seem to be a good indicator of how big the basic block is unless the
basic block is close to the beginning of the function. I think
MinNoSplitDisp should compute the distance between UserOffset and the
end of UserBB instead.
Added:
llvm/test/CodeGen/Thumb2/constant-islands-no-split.mir
Modified:
llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
Removed:
################################################################################
diff --git a/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp b/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
index 89eb49ed416ae8..e41e02a560db05 100644
--- a/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
+++ b/llvm/lib/Target/ARM/ARMConstantIslandPass.cpp
@@ -1323,7 +1323,8 @@ bool ARMConstantIslands::findAvailableWater(CPUser &U, unsigned UserOffset,
MachineBasicBlock *UserBB = U.MI->getParent();
BBInfoVector &BBInfo = BBUtils->getBBInfo();
const Align CPEAlign = getCPEAlign(U.CPEMI);
- unsigned MinNoSplitDisp = BBInfo[UserBB->getNumber()].postOffset(CPEAlign);
+ unsigned MinNoSplitDisp =
+ BBInfo[UserBB->getNumber()].postOffset(CPEAlign) - UserOffset;
if (CloserWater && MinNoSplitDisp > U.getMaxDisp() / 2)
return false;
for (water_iterator IP = std::prev(WaterList.end()), B = WaterList.begin();;
diff --git a/llvm/test/CodeGen/Thumb2/constant-islands-no-split.mir b/llvm/test/CodeGen/Thumb2/constant-islands-no-split.mir
new file mode 100644
index 00000000000000..9283ef14ca6cbe
--- /dev/null
+++ b/llvm/test/CodeGen/Thumb2/constant-islands-no-split.mir
@@ -0,0 +1,165 @@
+# RUN: llc -mtriple=thumbv7-linux-gnueabihf -run-pass=arm-cp-islands -arm-constant-island-max-iteration=1 %s -o - | FileCheck %s
+--- |
+ ; ModuleID = 'constant-islands-new-island.ll'
+ source_filename = "constant-islands-new-island.ll"
+ target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+ target triple = "thumbv7-unknown-linux-gnueabihf"
+
+ define void @test(i1 %tst) {
+ entry:
+ %0 = call i32 @llvm.arm.space(i32 2000, i32 undef)
+ br label %smallbb
+
+ smallbb: ; preds = %entry
+ br i1 %tst, label %true, label %false
+
+ true: ; preds = %false, %smallbb
+ %val = phi float [ 1.234500e+04, %smallbb ], [ undef, %false ]
+ %1 = call i32 @llvm.arm.space(i32 2000, i32 undef)
+ call void @bar(float %val)
+ ret void
+
+ false: ; preds = %smallbb
+ br label %true
+ }
+
+ declare void @bar(float)
+
+ ; Function Attrs: nounwind
+ declare i32 @llvm.arm.space(i32 immarg, i32) #0
+
+ attributes #0 = { nounwind }
+
+...
+---
+name: test
+alignment: 2
+exposesReturnsTwice: false
+legalized: false
+regBankSelected: false
+selected: false
+failedISel: false
+tracksRegLiveness: true
+hasWinCFI: false
+noPhis: true
+isSSA: false
+noVRegs: true
+hasFakeUses: false
+callsEHReturn: false
+callsUnwindInit: false
+hasEHCatchret: false
+hasEHScopes: false
+hasEHFunclets: false
+isOutlined: false
+debugInstrRef: false
+failsVerification: false
+tracksDebugUserValues: false
+registers: []
+liveins:
+ - { reg: '$r0', virtual-reg: '' }
+frameInfo:
+ isFrameAddressTaken: false
+ isReturnAddressTaken: false
+ hasStackMap: false
+ hasPatchPoint: false
+ stackSize: 16
+ offsetAdjustment: 0
+ maxAlignment: 4
+ adjustsStack: true
+ hasCalls: true
+ stackProtector: ''
+ functionContext: ''
+ maxCallFrameSize: 0
+ cvBytesOfCalleeSavedRegisters: 0
+ hasOpaqueSPAdjustment: false
+ hasVAStart: false
+ hasMustTailInVarArgFunc: false
+ hasTailCall: false
+ isCalleeSavedInfoValid: true
+ localFrameSize: 0
+ savePoint: ''
+ restorePoint: ''
+fixedStack: []
+stack:
+ - { id: 0, name: '', type: spill-slot, offset: -12, size: 4, alignment: 4,
+ stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+ - { id: 1, name: '', type: spill-slot, offset: -16, size: 4, alignment: 4,
+ stack-id: default, callee-saved-register: '', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+ - { id: 2, name: '', type: spill-slot, offset: -4, size: 4, alignment: 4,
+ stack-id: default, callee-saved-register: '$lr', callee-saved-restored: false,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+ - { id: 3, name: '', type: spill-slot, offset: -8, size: 4, alignment: 4,
+ stack-id: default, callee-saved-register: '$r7', callee-saved-restored: true,
+ debug-info-variable: '', debug-info-expression: '', debug-info-location: '' }
+entry_values: []
+callSites: []
+debugValueSubstitutions: []
+constants:
+ - id: 0
+ value: 'float 1.234500e+04'
+ alignment: 4
+ isTargetSpecific: false
+machineFunctionInfo:
+ isLRSpilled: true
+body: |
+ bb.0.entry:
+ successors: %bb.1(0x80000000)
+ liveins: $r0, $r7, $lr
+
+ frame-setup tPUSH 14 /* CC::al */, $noreg, killed $r7, killed $lr, implicit-def $sp, implicit $sp
+ frame-setup CFI_INSTRUCTION def_cfa_offset 8
+ frame-setup CFI_INSTRUCTION offset $lr, -4
+ frame-setup CFI_INSTRUCTION offset $r7, -8
+ $sp = frame-setup tSUBspi $sp, 2, 14 /* CC::al */, $noreg
+ frame-setup CFI_INSTRUCTION def_cfa_offset 16
+ tSTRspi killed $r0, $sp, 1, 14 /* CC::al */, $noreg :: (store (s32) into %stack.0)
+ renamable $r0 = IMPLICIT_DEF
+ dead renamable $r0 = SPACE 2000, killed renamable $r0
+ t2B %bb.1, 14 /* CC::al */, $noreg
+
+ bb.1.smallbb:
+ successors: %bb.2(0x40000000), %bb.3(0x40000000)
+
+ $r0 = tLDRspi $sp, 1, 14 /* CC::al */, $noreg :: (load (s32) from %stack.0)
+ renamable $s0 = VLDRS %const.0, 0, 14 /* CC::al */, $noreg :: (load (s32) from constant-pool)
+ renamable $r0, dead $cpsr = tLSLri renamable $r0, 31, 14 /* CC::al */, $noreg
+ tCMPi8 killed renamable $r0, 0, 14 /* CC::al */, $noreg, implicit-def $cpsr
+ VSTRS killed $s0, $sp, 0, 14 /* CC::al */, $noreg :: (store (s32) into %stack.1)
+ t2Bcc %bb.3, 0 /* CC::eq */, killed $cpsr
+ t2B %bb.2, 14 /* CC::al */, $noreg
+
+ bb.2.true:
+ $s0 = VLDRS $sp, 0, 14 /* CC::al */, $noreg :: (load (s32) from %stack.1)
+ renamable $r0 = IMPLICIT_DEF
+ dead renamable $r0 = SPACE 2000, killed renamable $r0
+ tBL 14 /* CC::al */, $noreg, @bar, csr_aapcs, implicit-def dead $lr, implicit $sp, implicit killed $s0, implicit-def $sp
+ $sp = frame-destroy tADDspi $sp, 2, 14 /* CC::al */, $noreg
+ frame-destroy tPOP_RET 14 /* CC::al */, $noreg, def $r7, def $pc
+
+ bb.3.false:
+ successors: %bb.2(0x80000000)
+
+ renamable $s0 = IMPLICIT_DEF
+ t2B %bb.2, 14 /* CC::al */, $noreg
+
+...
+# Check that smallbb is not split by the constant islands pass. Previously,
+# smallbb was split due to incorrect calculation of MinNoSplitDisp.
+#
+# CHECK: bb.1.smallbb:
+# CHECK-NEXT: successors: %bb.3(0x40000000), %bb.4(0x40000000)
+# CHECK-NEXT: {{^ $}}
+# CHECK-NEXT: $r0 = tLDRspi $sp, 1, 14 /* CC::al */, $noreg :: (load (s32) from %stack.0)
+# CHECK-NEXT: renamable $s0 = VLDRS %const.1, 0, 14 /* CC::al */, $noreg :: (load (s32) from constant-pool)
+# CHECK-NEXT: renamable $r0, dead $cpsr = tLSLri renamable $r0, 31, 14 /* CC::al */, $noreg
+# CHECK-NEXT: tCMPi8 killed renamable $r0, 0, 14 /* CC::al */, $noreg, implicit-def $cpsr
+# CHECK-NEXT: VSTRS killed $s0, $sp, 0, 14 /* CC::al */, $noreg :: (store (s32) into %stack.1)
+# CHECK-NEXT: t2Bcc %bb.4, 0 /* CC::eq */, killed $cpsr
+# CHECK-NEXT: tB %bb.3, 14 /* CC::al */, $noreg
+# CHECK-NEXT: {{^ $}}
+# CHECK-NEXT: bb.2 (align 4):
+# CHECK-NEXT: successors:
+# CHECK-NEXT: {{^ $}}
+# CHECK-NEXT: CONSTPOOL_ENTRY 1, %const.0, 4
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