[llvm] [AVR] 8 bit trunc regression (PR #152902)
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Fri Aug 22 03:57:23 PDT 2025
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
Author: Tom Vijlbrief (tomtor)
<details>
<summary>Changes</summary>
Fix https://github.com/llvm/llvm-project/issues/153156
See also https://github.com/llvm/llvm-project/pull/152028
---
Full diff: https://github.com/llvm/llvm-project/pull/152902.diff
6 Files Affected:
- (modified) llvm/lib/Analysis/InlineCost.cpp (+3)
- (modified) llvm/lib/Target/AVR/AVRTargetTransformInfo.h (+6)
- (modified) llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp (+7-2)
- (modified) llvm/lib/Transforms/InstCombine/InstructionCombining.cpp (+4)
- (added) llvm/test/CodeGen/AVR/issue-151080-mod.ll (+58)
- (added) llvm/test/CodeGen/AVR/issue-153156.ll (+90)
``````````diff
diff --git a/llvm/lib/Analysis/InlineCost.cpp b/llvm/lib/Analysis/InlineCost.cpp
index 757f68999691e..1b0710e09b0f9 100644
--- a/llvm/lib/Analysis/InlineCost.cpp
+++ b/llvm/lib/Analysis/InlineCost.cpp
@@ -1766,6 +1766,9 @@ bool CallAnalyzer::visitGetElementPtr(GetElementPtrInst &I) {
// This handles the case only when the Cmp instruction is guarding a recursive
// call that will cause the Cmp to fail/succeed for the recursive call.
bool CallAnalyzer::simplifyCmpInstForRecCall(CmpInst &Cmp) {
+ // FIXME Regression on AVR: github.com/llvm/llvm-project/issues/153156
+ if (!DL.isLegalInteger(32) && DL.isLegalInteger(8))
+ return false;
// Bail out if LHS is not a function argument or RHS is NOT const:
if (!isa<Argument>(Cmp.getOperand(0)) || !isa<Constant>(Cmp.getOperand(1)))
return false;
diff --git a/llvm/lib/Target/AVR/AVRTargetTransformInfo.h b/llvm/lib/Target/AVR/AVRTargetTransformInfo.h
index 0daeeb8f11cfe..e6862d8743bbe 100644
--- a/llvm/lib/Target/AVR/AVRTargetTransformInfo.h
+++ b/llvm/lib/Target/AVR/AVRTargetTransformInfo.h
@@ -44,6 +44,12 @@ class AVRTTIImpl final : public BasicTTIImplBase<AVRTTIImpl> {
bool isLSRCostLess(const TargetTransformInfo::LSRCost &C1,
const TargetTransformInfo::LSRCost &C2) const override;
+
+ TypeSize
+ getRegisterBitWidth(TargetTransformInfo::RegisterKind K) const override {
+ // default is 32, so change it to 16
+ return TypeSize::getFixed(16);
+ }
};
} // end namespace llvm
diff --git a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
index 6477141ab095f..88801a22ffa51 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp
@@ -1632,12 +1632,17 @@ Instruction *InstCombinerImpl::visitPHINode(PHINode &PN) {
return replaceInstUsesWith(PN, &IdenticalPN);
}
- // If this is an integer PHI and we know that it has an illegal type, see if
+ // For 8/16 bit CPUs prefer 8 bit registers
+ bool preferByteRegister = !DL.isLegalInteger(32);
+
+ // If this is an integer PHI and we know that it has an illegal type,
+ // (or 16 bit on 8/16 bit CPUs), see if
// it is only used by trunc or trunc(lshr) operations. If so, we split the
// PHI into the various pieces being extracted. This sort of thing is
// introduced when SROA promotes an aggregate to a single large integer type.
if (PN.getType()->isIntegerTy() &&
- !DL.isLegalInteger(PN.getType()->getPrimitiveSizeInBits()))
+ ((!DL.isLegalInteger(PN.getType()->getPrimitiveSizeInBits())) ||
+ (preferByteRegister && PN.getType()->getPrimitiveSizeInBits() == 16)))
if (Instruction *Res = SliceUpIllegalIntegerPHI(PN))
return Res;
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 5ee3bb1abe86e..bb4144ad109ca 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -311,6 +311,10 @@ bool InstCombinerImpl::shouldChangeType(unsigned FromWidth,
bool FromLegal = FromWidth == 1 || DL.isLegalInteger(FromWidth);
bool ToLegal = ToWidth == 1 || DL.isLegalInteger(ToWidth);
+ // For 8/16 bit CPUs prefer 8 bit.
+ if (!DL.isLegalInteger(32) && ToWidth == 16)
+ ToLegal = false;
+
// Convert to desirable widths even if they are not legal types.
// Only shrink types, to prevent infinite loops.
if (ToWidth < FromWidth && isDesirableIntType(ToWidth))
diff --git a/llvm/test/CodeGen/AVR/issue-151080-mod.ll b/llvm/test/CodeGen/AVR/issue-151080-mod.ll
new file mode 100644
index 0000000000000..e2981236482e6
--- /dev/null
+++ b/llvm/test/CodeGen/AVR/issue-151080-mod.ll
@@ -0,0 +1,58 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -O=3 -mtriple=avr-none -mcpu=attiny85 -verify-machineinstrs | FileCheck %s
+
+ at c = dso_local local_unnamed_addr global i8 0, align 1
+define dso_local void @mod(i16 noundef %0) local_unnamed_addr addrspace(1) {
+; CHECK-LABEL: mod:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: push r14
+; CHECK-NEXT: push r16
+; CHECK-NEXT: push r17
+; CHECK-NEXT: cpi r24, 10
+; CHECK-NEXT: cpc r25, r1
+; CHECK-NEXT: brlo .LBB0_2
+; CHECK-NEXT: ; %bb.1:
+; CHECK-NEXT: ldi r18, 205
+; CHECK-NEXT: ldi r19, 204
+; CHECK-NEXT: ldi r20, 0
+; CHECK-NEXT: ldi r21, 0
+; CHECK-NEXT: movw r22, r24
+; CHECK-NEXT: mov r14, r24
+; CHECK-NEXT: movw r24, r20
+; CHECK-NEXT: rcall __mulsi3
+; CHECK-NEXT: movw r16, r24
+; CHECK-NEXT: lsr r17
+; CHECK-NEXT: ror r16
+; CHECK-NEXT: lsr r17
+; CHECK-NEXT: ror r16
+; CHECK-NEXT: lsr r17
+; CHECK-NEXT: ror r16
+; CHECK-NEXT: movw r24, r16
+; CHECK-NEXT: rcall mod
+; CHECK-NEXT: mov r24, r16
+; CHECK-NEXT: ldi r22, -10
+; CHECK-NEXT: rcall __mulqi3
+; CHECK-NEXT: add r24, r14
+; CHECK-NEXT: .LBB0_2:
+; CHECK-NEXT: ori r24, 48
+; CHECK-NEXT: sts c, r24
+; CHECK-NEXT: pop r17
+; CHECK-NEXT: pop r16
+; CHECK-NEXT: pop r14
+; CHECK-NEXT: ret
+ %2 = icmp ugt i16 %0, 9
+ %3 = trunc i16 %0 to i8
+ br i1 %2, label %4, label %9
+4: ; preds = %1
+ %5 = udiv i16 %0, 10
+ %6 = trunc i16 %5 to i8
+ %7 = mul i8 %6, -10
+ tail call addrspace(1) void @mod(i16 noundef %5)
+ %8 = add i8 %7, %3
+ br label %9
+9: ; preds = %4, %1
+ %10 = phi i8 [ %3, %1 ], [ %8, %4 ]
+ %11 = or disjoint i8 %10, 48
+ store i8 %11, ptr @c, align 1
+ ret void
+}
diff --git a/llvm/test/CodeGen/AVR/issue-153156.ll b/llvm/test/CodeGen/AVR/issue-153156.ll
new file mode 100644
index 0000000000000..f9d08fc095d3f
--- /dev/null
+++ b/llvm/test/CodeGen/AVR/issue-153156.ll
@@ -0,0 +1,90 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: opt -Os -mtriple=avr-none < %s | llc -mtriple=avr-none -mcpu=attiny85 -verify-machineinstrs | FileCheck %s
+
+ at c = dso_local global i8 0, align 1
+ at ti = dso_local global i16 0, align 1
+
+define dso_local void @mod(i16 noundef %0) local_unnamed_addr addrspace(1) {
+; CHECK-LABEL: mod:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: push r14
+; CHECK-NEXT: push r16
+; CHECK-NEXT: push r17
+; CHECK-NEXT: cpi r24, 10
+; CHECK-NEXT: cpc r25, r1
+; CHECK-NEXT: brlo .LBB0_2
+; CHECK-NEXT: ; %bb.1: ; %tailrecurse.preheader
+; CHECK-NEXT: ldi r18, 205
+; CHECK-NEXT: ldi r19, 204
+; CHECK-NEXT: ldi r20, 0
+; CHECK-NEXT: ldi r21, 0
+; CHECK-NEXT: movw r22, r24
+; CHECK-NEXT: mov r14, r24
+; CHECK-NEXT: movw r24, r20
+; CHECK-NEXT: rcall __mulsi3
+; CHECK-NEXT: movw r16, r24
+; CHECK-NEXT: lsr r17
+; CHECK-NEXT: ror r16
+; CHECK-NEXT: lsr r17
+; CHECK-NEXT: ror r16
+; CHECK-NEXT: lsr r17
+; CHECK-NEXT: ror r16
+; CHECK-NEXT: movw r24, r16
+; CHECK-NEXT: rcall mod
+; CHECK-NEXT: mov r24, r16
+; CHECK-NEXT: ldi r22, -10
+; CHECK-NEXT: rcall __mulqi3
+; CHECK-NEXT: add r24, r14
+; CHECK-NEXT: .LBB0_2: ; %tailrecurse._crit_edge
+; CHECK-NEXT: ori r24, 48
+; CHECK-NEXT: sts c, r24
+; CHECK-NEXT: pop r17
+; CHECK-NEXT: pop r16
+; CHECK-NEXT: pop r14
+; CHECK-NEXT: ret
+ %2 = alloca i16, align 1
+ store i16 %0, ptr %2, align 1
+ %3 = load i16, ptr %2, align 1
+ %4 = icmp ugt i16 %3, 9
+ br i1 %4, label %5, label %10
+
+5: ; preds = %1
+ %6 = load i16, ptr %2, align 1
+ %7 = udiv i16 %6, 10
+ call addrspace(1) void @mod(i16 noundef %7)
+ %8 = load i16, ptr %2, align 1
+ %9 = urem i16 %8, 10
+ call addrspace(1) void @mod(i16 noundef %9)
+ br label %14
+
+10: ; preds = %1
+ %11 = load i16, ptr %2, align 1
+ %12 = add i16 48, %11
+ %13 = trunc i16 %12 to i8
+ store volatile i8 %13, ptr @c, align 1
+ br label %14
+
+14: ; preds = %10, %5
+ ret void
+}
+
+define dso_local void @t(i16 noundef %0) addrspace(1) {
+; CHECK-LABEL: t:
+; CHECK: ; %bb.0:
+; CHECK-NEXT: ldi r22, 57
+; CHECK-NEXT: rcall __mulqi3
+; CHECK-NEXT: mov r25, r24
+; CHECK-NEXT: lsl r25
+; CHECK-NEXT: sbc r25, r25
+; CHECK-NEXT: sts ti+1, r25
+; CHECK-NEXT: sts ti, r24
+; CHECK-NEXT: ret
+ %2 = alloca i16, align 1
+ store i16 %0, ptr %2, align 1
+ %3 = load i16, ptr %2, align 1
+ %4 = mul nsw i16 57, %3
+ %5 = trunc i16 %4 to i8
+ %6 = sext i8 %5 to i16
+ store i16 %6, ptr @ti, align 1
+ ret void
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/152902
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