[clang][AVR] Restrict range of assembly constraint 'G'

[benshi001]

According to https://www.nongnu.org/avr-libc/user-manual/inline_asm.html, "G" only represents floating point constant '0.0'. And avr-gcc also rejects other non-zero FP values.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Ben Shi (benshi001)

Changes

According to https://www.nongnu.org/avr-libc/user-manual/inline_asm.html, "G" only represent a float constraint "0.0". And avr-gcc also rejects other non-zero values.

---

Full diff: https://github.com/llvm/llvm-project/pull/76561.diff

3 Files Affected:

• (modified) clang/lib/Basic/Targets/AVR.h (+3-1)
• (modified) clang/test/CodeGen/avr/avr-inline-asm-constraints.c (+2-2)
• (modified) clang/test/CodeGen/avr/avr-unsupported-inline-asm-constraints.c (+1)

diff --git a/clang/lib/Basic/Targets/AVR.h b/clang/lib/Basic/Targets/AVR.h
index 854a51d78c393b..9376c46cd98ca1 100644
--- a/clang/lib/Basic/Targets/AVR.h
+++ b/clang/lib/Basic/Targets/AVR.h
@@ -146,7 +146,9 @@ class LLVM_LIBRARY_VISIBILITY AVRTargetInfo : public TargetInfo {
     case 'R': // Integer constant (Range: -6 to 5)
       Info.setRequiresImmediate(-6, 5);
       return true;
-    case 'G': // Floating point constant
+    case 'G': // Floating point constant 0.0
+      Info.setRequiresImmediate(0);
+      return true;
     case 'Q': // A memory address based on Y or Z pointer with displacement.
       return true;
     }
diff --git a/clang/test/CodeGen/avr/avr-inline-asm-constraints.c b/clang/test/CodeGen/avr/avr-inline-asm-constraints.c
index 96774861feb228..3a956de8db48f0 100644
--- a/clang/test/CodeGen/avr/avr-inline-asm-constraints.c
+++ b/clang/test/CodeGen/avr/avr-inline-asm-constraints.c
@@ -109,8 +109,8 @@ void R() {
 }
 
 void G() {
-  // CHECK: call addrspace(0) void asm sideeffect "subi r30, $0", "G"(i16 50)
-  asm("subi r30, %0" :: "G"(50));
+  // CHECK: call addrspace(0) void asm sideeffect "subi r30, $0", "G"(i16 0)
+  asm("subi r30, %0" :: "G"(0));
 }
 
 void Q() {
diff --git a/clang/test/CodeGen/avr/avr-unsupported-inline-asm-constraints.c b/clang/test/CodeGen/avr/avr-unsupported-inline-asm-constraints.c
index ceea59229f736a..29f0b69285fa88 100644
--- a/clang/test/CodeGen/avr/avr-unsupported-inline-asm-constraints.c
+++ b/clang/test/CodeGen/avr/avr-unsupported-inline-asm-constraints.c
@@ -5,4 +5,5 @@ const unsigned char val = 0;
 int foo(void) {
   __asm__ volatile("foo %0, 1" : : "fo" (val)); // expected-error {{invalid input constraint 'fo' in asm}}
   __asm__ volatile("foo %0, 1" : : "Nd" (val)); // expected-error {{invalid input constraint 'Nd' in asm}}
+  __asm__ volatile("subi r30, %0" : : "G" (1)); // expected-error {{value '1' out of range for constraint 'G'}}
 }

[SixWeining]

LGTM. I have checked with https://gcc.gnu.org/onlinedocs/gccint/Machine-Constraints.html. 'G' stands for "A floating point constant 0.0". But I'd like to wait others' opinion.

[jacquesguan]

LGTM