[clang] Fixes inf loop parsing fixed point literal

[PiJoules]

Clang was incorrectly finding the start of the exponent in a fixed point hex literal. It would unconditionally find the first e/E/p/P in a constant regardless of if it were hex or not and parser the remaining digits as an APInt. In a debug build, this would be caught by an assertion, but in a release build, the assertion is removed and we'd end up in an infinite loop.

Fixes #83050

[llvmbot]

@llvm/pr-subscribers-clang

Author: None (PiJoules)

Changes

Clang was incorrectly finding the start of the exponent in a fixed point hex literal. It would unconditionally find the first e/E/p/P in a constant regardless of if it were hex or not and parser the remaining digits as an APInt. In a debug build, this would be caught by an assertion, but in a release build, the assertion is removed and we'd end up in an infinite loop.

---

Full diff: https://github.com/llvm/llvm-project/pull/83071.diff

3 Files Affected:

• (modified) clang/lib/Lex/LiteralSupport.cpp (+6-3)
• (added) clang/test/Frontend/GH83050.cpp (+11)
• (modified) clang/test/Frontend/fixed_point_declarations.c (+18)

diff --git a/clang/lib/Lex/LiteralSupport.cpp b/clang/lib/Lex/LiteralSupport.cpp
index 571a984884029d..438c6d772e6e04 100644
--- a/clang/lib/Lex/LiteralSupport.cpp
+++ b/clang/lib/Lex/LiteralSupport.cpp
@@ -1513,8 +1513,10 @@ NumericLiteralParser::GetFloatValue(llvm::APFloat &Result) {
                                                : APFloat::opInvalidOp;
 }
 
-static inline bool IsExponentPart(char c) {
-  return c == 'p' || c == 'P' || c == 'e' || c == 'E';
+static inline bool IsExponentPart(char c, bool isHex) {
+  if (isHex)
+    return c == 'p' || c == 'P';
+  return c == 'e' || c == 'E';
 }
 
 bool NumericLiteralParser::GetFixedPointValue(llvm::APInt &StoreVal, unsigned Scale) {
@@ -1533,7 +1535,8 @@ bool NumericLiteralParser::GetFixedPointValue(llvm::APInt &StoreVal, unsigned Sc
   if (saw_exponent) {
     const char *Ptr = DigitsBegin;
 
-    while (!IsExponentPart(*Ptr)) ++Ptr;
+    while (!IsExponentPart(*Ptr, radix == 16))
+      ++Ptr;
     ExponentBegin = Ptr;
     ++Ptr;
     NegativeExponent = *Ptr == '-';
diff --git a/clang/test/Frontend/GH83050.cpp b/clang/test/Frontend/GH83050.cpp
new file mode 100644
index 00000000000000..df55d848a5fd5f
--- /dev/null
+++ b/clang/test/Frontend/GH83050.cpp
@@ -0,0 +1,11 @@
+/// This is the regression test for https://github.com/llvm/llvm-project/issues/83050.
+/// This just needs to compile.
+// RUN: %clang_cc1 -x c++ -ffixed-point -S %s -o /dev/null -triple=x86_64-linux -ffixed-point
+static constexpr unsigned short _Fract SQRT_FIRST_APPROX[12][2] = {
+    {0x1.e8p-1uhr, 0x1.0cp-2uhr}, {0x1.bap-1uhr, 0x1.28p-2uhr},
+    {0x1.94p-1uhr, 0x1.44p-2uhr}, {0x1.74p-1uhr, 0x1.6p-2uhr},
+    {0x1.6p-1uhr, 0x1.74p-2uhr},  {0x1.4ep-1uhr, 0x1.88p-2uhr},
+    {0x1.3ep-1uhr, 0x1.9cp-2uhr}, {0x1.32p-1uhr, 0x1.acp-2uhr},
+    {0x1.22p-1uhr, 0x1.c4p-2uhr}, {0x1.18p-1uhr, 0x1.d4p-2uhr},
+    {0x1.08p-1uhr, 0x1.fp-2uhr},  {0x1.04p-1uhr, 0x1.f8p-2uhr},
+};
diff --git a/clang/test/Frontend/fixed_point_declarations.c b/clang/test/Frontend/fixed_point_declarations.c
index 04ed25d227ca52..c8045767442739 100644
--- a/clang/test/Frontend/fixed_point_declarations.c
+++ b/clang/test/Frontend/fixed_point_declarations.c
@@ -125,3 +125,21 @@ long _Fract           long_fract_zero     = 0.0lr;    // CHECK-DAG: @long_fract_
 unsigned short _Fract u_short_fract_zero  = 0.0uhr;   // CHECK-DAG: @u_short_fract_zero   = {{.*}}global i8  0, align 1
 unsigned  _Fract      u_fract_zero        = 0.0ur;    // CHECK-DAG: @u_fract_zero         = {{.*}}global i16 0, align 2
 unsigned long _Fract  u_long_fract_zero   = 0.0ulr;   // CHECK-DAG: @u_long_fract_zero    = {{.*}}global i32 0, align 4
+
+// Hex exponent suffix with E in hex digit sequence.
+unsigned short _Fract e1 = 0x1.e8p-1uhr;  // CHECK-DAG: @e1 = {{.*}}global i8 -12
+unsigned short _Fract e2 = 0x1.8ep-1uhr;  // CHECK-DAG: @e2 = {{.*}}global i8 -57
+unsigned short _Fract e3 = 0x1.ep-1uhr;  //  CHECK-DAG: @e3 = {{.*}}global i8 -16
+unsigned _Accum e4 = 0xep-1uk;  //  CHECK-DAG: @e4 = {{.*}}global i32 458752
+unsigned _Accum e5 = 0xe.1p-1uk;  //  CHECK-DAG: @e5 = {{.*}}global i32 460800
+unsigned _Accum e6 = 0xe.ep-1uk;  //  CHECK-DAG: @e6 = {{.*}}global i32 487424
+unsigned _Accum e7 = 0xe.e8p-1uk;  //  CHECK-DAG: @e7 = {{.*}}global i32 488448
+unsigned _Accum e8 = 0xe.8ep-1uk;  //  CHECK-DAG: @e8 = {{.*}}global i32 476928
+unsigned short _Fract E1 = 0x1.E8p-1uhr;  // CHECK-DAG: @E1 = {{.*}}global i8 -12
+unsigned short _Fract E2 = 0x1.8Ep-1uhr;  // CHECK-DAG: @E2 = {{.*}}global i8 -57
+unsigned short _Fract E3 = 0x1.Ep-1uhr;  //  CHECK-DAG: @E3 = {{.*}}global i8 -16
+unsigned _Accum E4 = 0xEp-1uk;  //  CHECK-DAG: @E4 = {{.*}}global i32 458752
+unsigned _Accum E5 = 0xE.1p-1uk;  //  CHECK-DAG: @E5 = {{.*}}global i32 460800
+unsigned _Accum E6 = 0xE.Ep-1uk;  //  CHECK-DAG: @E6 = {{.*}}global i32 487424
+unsigned _Accum E7 = 0xE.E8p-1uk;  //  CHECK-DAG: @E7 = {{.*}}global i32 488448
+unsigned _Accum E8 = 0xE.8Ep-1uk;  //  CHECK-DAG: @E8 = {{.*}}global i32 476928

[nickdesaulniers]

For the commit message and PR description, please consider:

1. using a subject that describes more of what the patch does, such as "[clang] fixes inf loop parsing fixed point literal"
2. put "Fixes [clang] clang hangs when instantiate an array of fixed points. #83050" in the commit body; when merged, github will auto close the corresponding issue.